The chart below shows how the big three U.S. hamburger chains — Wendy's, McDonald's (MCD) and Burger King (BKW) — measure up in terms of sales recorded at company-owned locations only:

Source: SEC filings. Wendy's 2009 sales are for Wendy's/Arby's Group. Arby's was sold in 2011.

While new to Wendy's, the pretzel bun isn't itself a new invention. Other restaurants, either independents or chains, can be found that offer or have offered pretzel-type buns. One of those is Red Robin Gourmet Burgers (RRGB), based in Greenwood Village, Colo., which previously has sold a limited-time Oktoberfest Burger on a pretzel roll. It's also not the only case of baked pretzel dough being used to house meat: Pretzel chains Auntie Anne's and Pretzelmaker, for instance, carry pretzel dogs.

Brian Miller, the owner of Miller Baking in Milwaukee, started making pretzel buns for burgers back in the spring of 2007. In his view, the fact that so many people in the U.S. grow up with pretzels, and often having them during a leisure activity such as a trip to the ballpark or the county fair, helps the prospects for this type of bun.

"Americans have a really strong emotional connection with pretzels, soft or hard pretzels," he says. "There was just a natural progression to turn it into a bun."

Miller, who sells his products under the Pretzilla brand to individuals and retailers, including Whole Foods, sees an "absolute positive" with Wendy's move into pretzel buns, in that it helps make consumers aware that they exist as sandwich options. Various other types of pretzels, such as hard varieties, have of course been around for much longer than the rolls. "I'd like to believe that the interest level for a burger bun or a sausage bun is also going to have that kind of staying power," he says.

Should the Pretzel Bacon Cheeseburger carry a high price, and it very well may, it would be another entrant to the "barbell" strategy employed at fast-food restaurants, including Wendy's much larger rival McDonald's. By this, the chains offer a number of low-priced items with the aim of getting diners in the door, then hope they decide to buy a bigger-ticket item once there. For example, Carl's Jr. and Hardee's, both owned by CKE Restaurants, carry higher-cost fare such as the Super Bacon Six Dollar Cheeseburger. McDonald's, however, recently dropped its more expensive Angus burgers.

Beyond its direct competitors, the hamburger might enhance Wendy's position against the so-called better burger chains, names such as Smashburger, Five Guys and Shake Shack, that have entered the sector in recent years. Though much smaller in number than the giants, their growth indicates consumers want more variety than the national brands alone provide.