It slows down your RPM a little but smooth's out your power band. It's more noticeable when climbing steep rocky loose stuff and when hammering on flat sections. So far the main benefit has been no more sore knees.

 Thanks for your reply.
Sincs I race downhill, I am pedaling in very hard and short intervals. Do you think it would slow me down?

 Not at all. It improves traction due to it balancing out your power band of your pedal stroke. Fabian Barrel has been on them for a long time.

 So I would sprint faster? Also I use 36T round chainring, what size of oval would you recommend me?

 It would improve your traction so yes it would make you faster. I'd run a 36t like what you already have. The interesting thing about the way Absolute Black designs their oval direct mount rings is that they actually add 2 teeth on the tall side and subtract 2 on the small side. I'm on a 32t which translates to a 34t on the tall side and a 30t on the small side. The effort feels like a 33t ring. I would imagine that it would be a little harder to push the same tooth count ring in an oval but the added benefits would be worth the change.

 It's been a weapon of choice for road bikers for many years. Look up a company named Rotor.

 Glad to help dude! Rubber side down!