That is a rheostat it will need to be adjusted every time the room temp changes. They work really well in absolutely stable room temps. It is for you to decide what your room is like. Generally speaking they are not useful out side a snake room that has dedicated heating and cooling to maintain constant temps.

No a proportional is not necessary it is the most versatile and will work exactly as expected under the most varied conditions. I think the herpstat lists at 104 or so. You could go with a ranco, or johnson they are in the 50$ range and the hydrofarm is 40$ or so all three like semi stable room temps and don't do really well in rooms that are not too cooler than the set point. I'd suggest that if you go that route especially with the hydrofarm then attach the uth to a sheet of glass and then place the tub on that to absorb the possible spikes.