I feed a mix of prekilled soft furs, prekilled mice (mainly for the smaller snakes), and FT rats. No issues with anyone getting fussy. They'll just about all eat anything I dangle in there as long as it's warm enough.
I've even used them exclusively to get problem eaters chugging along, then had no trouble getting them to take other items.
I think there may be a few animals out there that might show some preference, but for the most part it's just not true. Not that I've experienced.