I can relate to this. When the Shimano crankset with this type of crank arms first came out, I upgraded to it. To ensure it was installed properly, I let the bike shop install it. After one short ride, the crank arm fell off. I was so furious, I went back to the bike shop and demanded they reinstall my old crankset and refund my money. I upgraded later to a Campy Record crankset with hirth coupling.