a CHE and a heat bulb such as a red bulb or daylight bulb pretty much heat up the ambient temperature inside an enclosure and both types do not emit any UVB radiation although unlike the CHE, the bulbs will light up the enclosure in some way. i think mercury vapor bulbs emit heat, light and UVB but they are usually very strong and not necessarily needed/used with snakes.

i think that the UTH would be more spot oriented than a bulb or CHE because they can raise the ambient temperature of the entire enclosure where as UTHs only create a surface temperature for a basking spot and raise only the ambient temperature above it by a few degrees.

i think flexwatt and UTHs are pretty much the same thing and are used the same way with a thermostat.

if you have a room temperature that doesnt fluctuate too much and meets the low end of your snakes needs then just a UTH or flexwatt will do but if the room is too cold then you will need to raise the enclosure's temperature with a bulb or CHE, for example.

hope this helps.