From what I learned here I decided to try and switch Pretzel over to rats. I was worried about it because he has been a fantastic eater so far with mice and I didn't want to screw him up. I shouldn't have worried! He took it within a few seconds me me dangling it in his cage.
I am really happy with him as the breed (royal constrictor designs) said that he is a good eater, and they definitely didn't lie!