I have both--- I have a few racks with back heat-- the ones we built first-- less wiring-- and I was less paranoid about them.
Now we've got a few with belly heat... I don't like that the tub actually contacts the flexwatt-- makes me worry as I've had bad previous experiences with that....
I see no difference in the way anybody eats, poops or sheds... the ones with back heat hang out at the end of the tub to digest--- and at the front other times... water is in the middle...
I say-- if the price is right-- get the racks...
I don't see any differences in behavior between the 2...
~Beth
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The rescue site: www.freewebs.com/okreptilerescue