They work great with the UTH but poorly with Flexwatt. With flkexwatt I was constantly adjusting but with my UTH I never have to touch the dial unless I have a temp swing in the 6-10 degree range which never happens thanks to my space heater. But flexwatt... yeah the reptitemp will not hold a steady temp.
Yes, you can rely on it. I have left my guys for over a week with it and when I came back, the temps were exactly like I left em.
Pros-cheap, reliable, easy.
Cons- Cheap, not digital, may have to be adjusted once in a awhile.