You know, I've been thinking that the CM901 was the closest thing to the TAR-21 of the game, since it was released. The underbarrel glitch was great for the weapon, even if it made the SCAR-L and the AK47 useless (to me).
I'd love for the underbarrel glitch to return as the standard (like it did with the Extended Mags glitch with Shotguns, for the USAS 12). Right now, though, the closest thing to the TAR-21, is the G36C, but I personally don't care for the completely vertical recoil (It's too damn high. See what I did there?).
The CM901 either needs a buff, or it may as well not have been included in the Multiplayer, because it really is that bad.