all fins intact is very good for you, as if they break and go 'down the food chain' they can cause BIG problems. btw, i highly reccomend you pick up a spare or two just to keep onboard. getting to know your engine isnt a bad thing by any means, just a bit of a learning curve. ive got a spare onboard and will check the flexiblity factor out for you but dont know how scientific i can be. IIRC last one i replaced i would rate at 'medium flex' 1=low flex 10=max id rate it at 3 or 4.
this link is failing me but may work for you:
Albin Motor
AHA! This one looks good--the manual:
AD-21 Handbook