The concern about any RF is going to be twofold: Is there any congestion, and what's it's dispersion. Higher frequencies are not going to penetrate masses as far (like bodies, walls etc) and as such are a bit more 'line of sight'... and that must be considered. In terms of congestion: are the other RF sources predictable? Will it work in rehearsal, but when you fill the room with audience with 2.4GHz wifi (the number of people constantly running their phone as a hotspot always surprises me). What uses 1.8GHz? Dect phones, (less common) but also increasingly I've noticed micro-controller type systems that use them for short range comms... About 5 years or so, at a PLASA I was chatting to someone from Sennheiser about wireless microphones. I was asking about whether they thought they were ever going to go down the digital route (as an Electronic Engineering student at the time, I was learning about the technology that made it possible). I was musing on the possibility of more channels in a given bandwidth, better coping with noisey RF situations etc. I was shot down and laughed at by the man... and told in no uncertain terms that Sennheiser would never go digital, and always be analogue, as digital would never give a good enough audio quality. Funny that.