Reliability with full power slugs and buckshot, which is all that I have used so far, is flawless.
The light mount is an ARMS 21 scope ring with ARMS 22TRC and 1" adapter, attached to an ARMS 22TRR Tactical Ring Rail. The 22TRR provides the picatinny surface for the Surefire throwlever attachment of the 12V Millenium light.
This was initially a temporary setup, as the ring has to be removed from the mag tube to remove the barrel. However, Surefire now says that they have no plans for a mount for the Benelli M1014/M4.
A better solution seems to be the mount available from Sidearmor.