Hi Nigel I use them all the time. The latest is just a small bud cheek mic that looks like a wart on your face....but sounds brilliant.
Here is a link with advice and info on wireless systems.
http://www.sweetwater.com/shop/live-sound/microphones/wireless_buying-guide.phpMost quality makes do a headset radio mic so buy what brand you prefer using.
Important things to consider are the quality of signal and signal range, diversity, Whether it is a licenced wavelength or not.
I do not know about the US but here in UK we have licenced and unlicensed wavelengths. Licenced means that this band can only be used by the licensee. Non licenced means that anybody like taxis, radio controlled toys etc etc etc can use the same wavelength. Most of the top makes use licenced so you do not get interference from these other apps. Nothing more embarrassing than "car 49 where are you" in the middle of a gig LOL
Shure and Audio Technica systems are licenced so that is what I would recommend.
As far as quality of sound is concerned they are as good as the wired models. Price wise start around £100 about £250 for a quality Shure system.