I have never owned a 391 - all I can tell you is this system is very simple to clean. On the Xplor, which handles 2-3/4 to 3-1/2" ammo, there is nothing to readjust to shoot any ammo. (As light as the gun is, I would opt for the Kick Off system to help the gas system attenuate the recoil. My understanding of the 390 and 391 systems is that both were somewhat difficult to clean. This does not appear to be as big an issue with the A400.
It is high on my recommend list, even though I favor O/U and SxS primarily - great back-up/rainy day/loaner type of gun