I've never run an M4, but I did see an M4 choke and puke all through a Steve Fisher class while 3 1301s ran like sewing machines throughout... I'm not saying the M4 isn't good, just that particular M4 had significant function issues that day.
I've been running my 1301T Gen 1 for several months now with well over 1000 rounds through it -- everything from 30-year old reloads to 100-pack cheapo birdshot to Federal Flight Control buckshot -- and it's run it all with no issues. Add Aridus SGA stock adapter, a CROM with a T1 and a Zukov forend and you have a great gauge...