It's fine, it allow players to actually prove that they were teamhit on the spawn so admin can ban the teamhitter. Also, if admin witness someone who abuse it (it's fairy easy, you know who your teammates are) clicking m in the heat of battle, he can warn and kick those guys too.
I played few hours with it and was reported twice, once for glancing blow on some sb my old friend (who killed the target and i was unable to stop the attack) and once by Ariec, whom i hit 3 times (not on purpose, 2 glancing hits and 1 overhead, happens). I reported only people who teamhit me on spawn or with no enemy nearby, despite the possibility to report other people.
Give it a few days, people will get used to it and don't spam it (except trolls, but you can't fight with them).