worthwhile yes, its more about the increased driveability than the power gain. my 172 has had development work on, and altough power gains arent very high, the overal driveability makes me feel like the car is going 2x as fast!
get them to gaurantee the power increase tehn prove it when done, as capt says, then you can get it free is they dont delivcer what they promise, or they will do teh extra work to find that 11bhp....which will be hard