Let me admit my bias right up front: I’m a nut about my Fitbit (FIT).

My little Fitbit Alta does an incredible job of turning invisible aspects of my health—sleep cycles, heart rate, activity levels, and so on—into motivating graphs and coaching. And Fitbit’s phone app provides even more inspiration by showing my wife’s, my father’s, and my friends’ data alongside my own. There’s nothing like health through humiliation.

But according to the sales figures, not everyone is so enthusiastic about fitness bands. Nike (NKE) discontinued its Fuelband in 2014. Jawbone Inc. shut down this year. Microsoft (MSFT) discontinued its fitness band in 2016. (“It’s a tough category,” Microsoft CEO Satya Nadella told me. “Brutal.”)

And Fitbit itself is struggling. Its stock is at roughly $6.50 a share—down about 85% from its 2015 peak. It laid off 110 people earlier this year.

The common wisdom is that smartwatches are what’s eating Fitbit’s lunch. A lot, therefore, is riding on the new Fitbit Ionic, Fitbit’s first actual smartwatch, which costs $300.

(Wait—wasn’t last year’s Fitbit Blaze supposed to be a smartwatch? Kind of, but the Ionic is far more developed. It has its own operating system and app store, plus GPS, water resistance down to 50 meters, swim tracking and lap counting, 2.5 gigabytes for storing music to play during your runs or workouts, and auto-recognition of 20 different exercises.)

The Ionic is a terrific fitness watch. And here’s the headline: five-day battery life. (Take that, Apple Watch and your puny one-day battery!)

But as a smartwatch, the Ionic is bizarrely weak.

Ionic fitness

The Ionic, to me, looks huge. It’s incredibly light, and fairly thin, so its size isn’t a practical problem—just a cosmetic one. It’s a vast aluminum square (in silver, gray, or orange), flanked by trapezoidal tabs.

Two buttons on the right, one (the Back button) on the left; navigation is easy. It’s waterproof, even for swimming and diving, and the two band halves are very easy to detach when you want to change straps, although the strap catalog is pretty small: your choice of plastic, perforated plastic, or leather. The colorful touch screen is super bright, even in direct sun—no problems there.

When it comes to tracking your health, the Ionic is a champ. It tallies your steps, calories, and distance; flights of stairs you’ve taken; minutes of exertion; continuous heart rate; and your stages of sleep, which is remarkably accurate and informative.

(You know how sometimes you can remember your dream, and sometimes you can’t? The Fitbit reveals why—it’s when a REM cycle slams right up against a wakeup moment.)

Underneath, the heart-rate sensor has gained a new, third LED light, capable of detecting how much blood oxygen you’ve got (your relative SPO2). Someday, that statistic could provide early detection for conditions like atrial fibrillation or sleep apnea, which would be a huge deal for millions of people.

The Ionic has built-in GPS—indeed, it’s the lightest GPS watch available, Fitbit says—so it can track the actual path of your runs or bike rides, and share that data with popular running apps like Strava.

On any smartwatch, GPS is usually turned off, because it’s a battery hog. Fortunately, you can set up the Ionic so that it turns on GPS automatically when you begin a run. Unfortunately, it’s not at all clear how you set that up. (Hint: Open the Exercise app. Open the Run module. Open the gear icon. Turn on Run Detection. Turn on GPS. Return to the Home screen.)

From now on, once you begin a run, the Run app will open automatically (well, after you’ve been running for five minutes) and begin logging your pace, distance, and split times—and the GPS will automatically power up and track your route and elevation.

The Ionic is also smart enough to pause the clock when you have to stop at an intersection, so those micro-layovers don’t mess up your split times. Works great.

Ionic the Smartwatch

Is the Ionic, in fact, a smartwatch at all? I guess it depends on how you define that term. Smartwatches from companies like Apple and Samsung usually offer features like these:

• Choice of watch faces. Maybe you like digital, or analog, or elegant, or complicated. On real smartwatches, you can choose from dozens of watch faces, or even design your own, and you can swap them whenever you like. On the Fitbit, though, you have a choice of only 17. You can’t edit them. Worse, you have to choose them from the phone app (not on the watch)—and making a new selection involves an interminable Bluetooth transfer that can take several minutes.

• Notifications. Smartwatches can notify you on your wrist whenever one of your phone apps is trying to get your attention (you choose which apps). That’s especially useful when incoming calls and texts arrive—but on the Ionic, you can’t respond in any way; there aren’t even canned shortcut responses like “I’ll get back to you.” Scrolling through your recent text threads on the watch reveals a weird, one-sided script containing only the other guy’s utterances—none of your own.

• Music. You can load about 300 songs onto the Ionic, for playback through Bluetooth wireless earbuds when you’re working out (Fitbit even sells its own pair, although you can also enjoy any of the 40 models I reviewed here.) But you must load them from your computer using a crude Mac or Windows app called Fitbit Connect; it shows only playlists, not songs or albums. There’s also a Pandora app, but it requires a paid subscription. There’s no Spotify.

• Voice assistants. On real smartwatches, you can speak to Siri or the Google Assistant, and hear spoken replies. The Ionic has no speaker or microphone, so it can’t do any of that (unless you buy Fitbit’s earbuds).

Still to come

Part of the Ionic’s promise has yet to be fulfilled, because Fitbit Inc. is still working on it. For example:

• Apps. On real smartwatches, you can choose from hundreds of cool little apps to run on your wrist. At the moment, there are only 11 apps available for the Ionic, and they’re all slow and very simple. Fitbit says that a full-blown app store will open later this year, with many more apps, but there’s no way to see it now.

• Fitbit Pay. In theory, you can pay for things with your Ionic, much as you pay at wireless terminals using an Apple Watch. At the moment, though, this feature is very limited—the only brand-name banks that offer it are American Express, Bank of America, Capital One, and U.S. Bank. It works great if your credit card comes from one of those banks; otherwise, Fitbit has a lot of work to do.

• Guided workouts. Fitbit bought a company called Fitstar last year, and already, you can pay $40 a year to use its guided video workouts on the Fitbit website or on your smartphone. Fitbit says these workouts are customized—they adjust their intensity based on your own feedback. Eventually, these coaching sessions will be available on the Ionic itself, although only in audio form.

The buying calculus

People with Apple (AAPL) and Samsung watches miss out on one of the best aspects of a fitness tracker: recording your sleep cycles. That’s because during the night, your watch is not on you. It’s on your bedside table, charging, thanks to that lousy one-day battery life.

But the Fitbit Ionic routinely gets five days from a charge, and that’s a big, big deal. (You charge it by snapping in a tiny cord connector into its back.)

The trouble is that a non-cellular Apple Watch Series 3 costs only $30 more than the Fitbit, and does much more. It runs faster, looks better, runs hundreds of apps, has Siri, lets you respond to calls and texts, offers magnetic charging, and so on. If you’re in the market for one of these things, then, the question is: Are you willing to sacrifice all of those nice features to get sleep tracking and five-day battery life?

I appreciate Fitbit’s strategy here—trying to save itself by competing with the very smartwatches that are cutting into its sales. But as a Fitbit fan, it bums me out a lot to say it: The Ionic may be a spectacular fitness watch, but its weakness as a smartwatch make it unlikely to be the grand slam the company desperately needs it to be.

More from David Pogue:

Augmented reality? Pogue checks out 7 of the first iPhone AR apps

iOS11 is about to arrive — here’s what’s in it

MacOS High Sierra comes this fall—and brings these 23 features

T-Mobile COO: Why we make investments like free Netflix that ‘seem crazy’

How Apple’s iPhone has improved since its 2007 debut

Gulliver’s Gate is a $40 million world of miniatures in Times Square

Samsung’s Bixby voice assistant is ambitious, powerful, and half-baked

Is through-the-air charging a hoax?

David Pogue, tech columnist for Yahoo Finance, is the author of “iPhone: The Missing Manual.” He welcomes nontoxic comments in the comments section below. On the web, he’s davidpogue.com. On Twitter, he’s @pogue. On email, he’s [email protected]. You can read all his articles here, or you can sign up to get his columns by email.