I've got one and like it.
Since the one your looking at is second hand, it depends how old it is as to which heater it's got. Mine is two and a half years old and came with the heater that has no temps marked, only + and -. It was no problem finding exactly where to set the knob for the temp I wanted.
However, after not quarantining some new fish, I ended up with ich. The treatment says to incease the temp, but even on maximum, it wouldn't go hot enough! So I got a different make. The Juwel one still works fine for normal temps, so I'm keeping it as a spare, just in case!