I have done many mid-length gas systems on 14.5" barrels -- it is, IMHO, the only way to go. Reliability is what you would expect from the mid-length system and the benefits of the system are the same.
The first prototype is still in use and has an untold number of thousand rounds through it now and I have not heard any complaints from anyone that has borrowed, used or otherwise nicked it for a few days.
Rate of fire is more where it should be... I like the system quite well. I have posted pictures of the dissy style "Recon Rifle" top end on here several times (mid-length, 16", full length hand guards)... but the mid-length 14.5 systems (some have seen the Aardvark) have not been shown much.
Maybe this week I can get the okay to post pictures of the two top ends -- they will be at the end of this link www.midlengthuppers.com
But, the Enhanced Battle Receiver... well another time.