I use those, the mediums, for both of my BP's, and I have two of the smalls that they stopped fitting into and still tried to use. I think they're great. My snakes love them, and my male BP actually moves his around his tub to where he wants to be - sometimes it's half on the heat, then I'll see him slithering around inside and it slides over all the way on the heat again. I'm not entirely sure that it's intentional... but it certainly looks like it is!