I have the Varrox, which is a high quality device:
However, I don’t use it much any more, because as i mentioned, I do this instead:
I don’t have a FH2 screened bottom board under my hives, yet… Maybe @chau06 does? What I do with my FH classic is cut a piece of roofing flashing to fit in the slider slot, then rest the Varrox on that, closing up the gap at the back with some old tea towels. Works just fine doing that way, vaporizing the OA below the screen. 