im using the 500R on two cages right now. i have it on my chondro cage and its ok...just ok. for the ball setup im using a UTH and tried placing the probe directly on the UTH and can't get the temps high enough. tried again last night right after this happend and could only get the temps up to 84ish with the stat on full blast. it kept kicking off before it would reach any higher temp. so my probe is attached to the thermometer in the warm end of the tub. it was working great until last night. its working fine now. not sure why it did that. the probe was in the same place as before.

the biggest problem i have with them is the temp swing. it goes from 89 down to 85 before it kicks on again. thats too much IMO. correct me if im wrong but the proportional ones shouldn't have that kind of variance.