FMJ's IMO are one of the top arrows out there. Something that hasn't been addressed is how beneficial the aluminum outer layer actually is.
Everyone (or at least almost everyone) that has shot carbons has experienced an arrow that seems undamaged but for some reason just doesn't hit the mark or fly well. Carbons can have flaws that are undetectable to the shooter but only show up in flight issues. The aluminum wrap on FMJ's will show any significant trauma the arrow has experienced because of it's inability to go back to shape like the carbon.
Many people will say "then just shoot aluminum"....however, carbon arrows wrapped in aluminum are not only much stronger than aluminum alone but also offer the other benefits of carbon. (tunability, longevity, penetration)
I'm pretty hard on my equipment and can honestly say that I've been impressed with the durabilty of FMJ's. When a dozen arrows lasts me years, I can't complain.....Ryan