Most under tank heaters suck. I use a large size one from Bean Farm, they make the very best UTH's and keep it
regulated to 85-90F using a digital thermometer with probe taped directly to the pad and a lamp dimmer to
control the temp.
I have been keeping reptiles for many years and have tried every brand of UTH on the market. Trust me, most of them
are worthless!! esp the ones that have a "sticky" peel off backing which, once mounted, can not be easily removed.
The Bean Farm pads have no sticky backing, and are made to never go above the mid 90's F. So depending on your
needs, it does not require a thermostat or dimmer because the temp will never "run away" and go up to 120F, cooking
your reptiles!!!! they are also reliable and last for years!!
Believe me, I have thrown a lot of cheesy UTH's in the trash (ZooMed, Zilla and Exo-Terra included!!)
I also use a infrared thermometer to regularly check the actual temps inside the cages.
Problem with me is, I stack my 12'' net cubes, so the cubes up top are always a few degrees cooler, though they
are always in the mid 70's at night and low 80's in the day.
I think it's important to have some air curculation too, so I keep a fan running on the far corner (way away from the mantid
cages) of the room.
Mantids wont eat if they are cold