Well, my new Elite CAR A4 middy has over 800 trouble free rounds through it so far. Just like my Glocks, it just works! Besides the aesthetic advantage the middy has with the barrel looking more appropriate, I just couldn't find a good grip point on the short handguard of the carbines. In addition, the the middy produces a less sharp very recoil impulse much like the full size gas system ARs.
In addition, it may only be a small point, but I also appreciate the small delay in start of the cycling that the middy enjoys over the carbine's gas system. I just think that a later cycling action is inherently more safe. The later model M-1 Carbines went with a different operating rod cam actuator design for that very same reason. YMMV.