if you have any doubt in your mind , if a mechanical will work or not, then you should not use them.

Mechanicals will work, better, out of a well tuned bow. for setups with KE in the 55 ft lb range don't go any larger than 1 1/4 inch cut.
A two blade offers less resistance than a three blade therefore a two blade should penetrate better than a three blade.

Like any other broadhead they will not make up for bad shot placement.

Most stories about mechanical broadhead failure is bad shot placement, even though the teller of the tale will deny it.