The Airsal is a good cilinder. Think it can be compared with the Due+.
The performance is somewhere inbetween of the Stage6 Sport pro and Stage6 Racing. So 12-13BHP is possible. Exhaust tip: Giannelli shot or Yasuni C16.
It has a bridged exhaust port, so higher wear on the rings. But since this cilinder isn't that high revving, this shouldn't be a problem.
In the past these Airsal's had a poor finishing. If you buy it, take a good look at the ports. If necesary, bring it to a tuner to have it finished.