I have had a Zaon XRX PCAS for about 25 hours now. It's very good and the previous complaints I'd heard about it showing traffic which doesn't exist don't seem to be accurate. Height and position are generally pretty accurate - range is less so, particularly when things get close by. It does need external power, so I've had a power cable put in that comes out the top of the dash. Hooking it up to the 496 is a bit of a gimmick really; nice but definitely not necessary.
I wouldn't go as far as to say I wouldn't fly without it - there are too many non-transponding aircraft around for that to make any sense. But yes, it works well.