We made some monstrous burgers. Seriously. I couldn't fit one in my mouth without some serious squishage. The reason ours turned out so huge is because we freeze our ground beef in 1/4 pound hamburger patties, so when we sandwiched the two patties around the feta it was larger than what the recipe called for. (1/2 lb instead of ~1/3 lb).
Still, they were pretty good, especially the bacon part. In addition to what the Martha Stewart recipe (found here) called for we added mayonnaise (me), pickles (Kyle) and red onion (both). If we made them again we'd cut down on the feta a little. Otherwise, a fun new burger combo!