I have one that came on my Pro-X and I think it's fantastic. I don't believe I've shaped it in the 6+ months I've had it. I've heard of others complaining that it hardens and I believe some have trouble with it popping off. No issues for me.
I've played with Everest, Sniper and Onyx from Tiger.
Only the Onyx I can truly recommend.
The Everest starts out OK, but after ~3-4 months suddenly gets just uncomfortably hard and feel-less, dead and hard. Lots of shaping, roughing, .... Don't get it, it's cheap mass medium tip.
The Sniper is good for about 6 months, then needs some serious roughing up. In the beginning is very nice, grippy, a bit bouncy, great feeling.
Then it also gets harder and a bit feelless.
Extremely (really extremely) consistent on each layer, no warping, no mushrooming, no shape problems, but gets a bit flat in the middle so you need to round it from time to time. Holds chalk well.
Onyx is a slightly softer Sniper and holds the softness better. Also being black it looks fantastic. Very grippy and nice.
I use Ultraskins now, very similar to the Onyx somehow and much cheaper.
Cheers,
M