I happen to own several of the RBI Plastics racks. Three with back heat and one with belly heat. The smaller racks come with back and the CB70 size rack with belly heat. The back heat is provided by an 11" strip of heat tape while the belly heat is provided by two seperate strips of 3" heat tape recessed into the bottom of each shelf. They come prewired and are ready for a thermostat, just plug and go. I personally prefere the back heat as it seems to heat the entire rear area of the tubs to 86 deg. (which are included by the way, all you have to do is drill a few vent holes) including the air temp. With the large CB70 the heat is very localized to the areas right over the heat tape, which I am sure will be perfect for when you want to start a cool down, but still provide a basking area. My females are still a little small and I would like to keep them feeding all winter long, so the more constant heat gradient from front to back is what I am looking for. I do not have a dedicated, climate controled room at this time, so the air temps at the front of the tubs are the same as the temps in my house, 82 deg. in the summer and 75 deg. in the winter. I bought the Ranco prewired thermostats that RBI offers, they are definatley less expensive, but not cheap, all though the clicking off and on can be annoying especially at night (Didn't last long in the bedroom). As far as controlling the temps they run with a 1 deg. or - variant so the temp stays fairly constant, at least for maintenence temps. The racks them selves are very well constructed and come preassembled and ready to use and the tubs fit very snug(had to sand a few down on the bottom). I don't know what your future plans are but for a first, second or third rack you can go wrong with these, and the price is great. Hope this helps you make your decision. I know I am very satisfied with mine.
Jeff