All right, I'll put my hand up. I've used one during an emergency, when the fan on the Jabbie went quiet. GME MT410G. Quick and easy to deploy on final approach, as we were in unfamiliar terrain with sparse scrub and about 16 km from the nearest road.
Had a Virgin RPT overhead within 15 minutes, and a rescue chopper was on scene within 2 hours. An excellent outcome - no injuries and no damage to the aircraft (apart from a dead donk). We did offer to walk out, but the S&R authorities were having none of that.
As a bit of a tangent, neither pilot of the Virgin RPT were able to spot us during any of their three passes, but several passangers did. Apparently we caused a bit of excitement amoungst the pax!
Back to the main story. As this was a genuine emergeny, AMSAR replaced the EPIRB free of charge - very kind of them.
Information from AMSAR during the debrief was that because we had used a GPS based EPIRB, they were able to locate us to within 100 metres in just three minutes.
In the same scenario with a non-GPS equipped EPIRB, the typical location time is upwards of 4.5 hours and then only to a radius of five km. Those extra 60 bucks for a GPS equipped EPIRB was very cheap. Worth it's weight in gold if there were injuries.
The GME EPIRB was simple to operate, just lifted the antenna and showed it to the sky while we were preparing to land. I would not like to try and activate some of the smaller ones in a hurry, that require buttons to be pressed etc.
Whatever EPIRB you choose, make sure it is super simple to operate (I can't emphasise that enough) and GPS equipped. Aint worth a pinch of you know what otherwise.