I like my tif ZX-1 and have to assume the ZX is the same deal except it looks less like the
one eyed one horned purple people eaters unit :-/
Mine picks up small HFC leaks with no problem. The kind of leaks the you need to stare at soap bubbles with a flashlight and mirror for a while to pinpoint the source!! I'll take it up on a windy roof and not worry too much about it either.
There was a place I go with a stationary engineer that has a small rack they switched to a HFC that they had been gassing up and asked me to leak check. I went through everything and noted locations of all the leaks I found and he thought I was full of BS lol.
Also over the years I have found you can search in high concentrations as well with out damaging sensitivity. I have drown mine in refrigerant too many times to count and it still finds the tiny leaks.
If you are using it and it starts screaming on a big leak there is a arrow button that zeros for that concentration and it will hit again the closer you get to a leak.
There are a few patents on that detector so it IS different than other heated type detectors and is not even close to that SRL2 that I still keep for when the ZX-1 is on the charger. I should really get a back up ZX since nothing else looks like like I'm going to be happy with that I can find out there.