The sandwiches feature hickory-smoked bacon, caramelized grilled onions, two slices of white cheddar, and a creamy mustard sauce along with their respective bases (third pound Angus beef patty, or grilled or crispy chicken breast).
Pricing on the burgers comes in at $4.79 regardless of which version you choose.
The white cheddar isn't actually cheese, but instead pasteurized process cheese product (think American cheese). It's good for melting and generally cheaper than real cheese.
The sandwiches were previously tested earlier this year in South Florida (although at a lower price: $4.49).
For a review, check out this one from California-to-New-York-transplant food blogger, An Immovable Feast.
Update 9/22/12: The Cheddar Bacon Onion Angus Burger and Chicken Sandwich will roll out nationally for a limited time this fall (look for late October to early November). Of course this pushed the McRib's limited time run well into December...
