Tried it on Timo Boll Spirit blade for ~2-3 month on my FH side
It was very linear and very predictable rubber, producing exactly what you put in it, not helping in some aspects, but not bothering too. Every type of stroke was somewhat above average, nothing extraordinary. I liked its feedback very much. Guess it had some speed limit, but I wasn't hitting it to often (however I had a feeling that I'm very close to it, maybe a false one). And also I would like a little bit harder rubber with a higher throw.
The only real problem for me was counter-looping. I simply couldn't get used to its throw angle. I could adjust it during training sessions, but it was too hard for me to use on tournaments. That's more about my strokes and my habits, but I couldn't change them, unfortunately.
The second problem, which I could live with was its durability. I felt that sponge was slowly dying, getting softer and more wobbly/like cottonwool or something like that (have no idea of an English word I can use here). I used to train around 8-10 hours / week those days, and first month was good, second month was with some problems and the third month I've been simply waiting for replacement to arrive.