I have had mine for a year now. I have the compcarrier titanium tube and enough US made parts as is required. It has never failed to fire any type of ammo I have fed it. It is not as fast as the M1 and M2 designs but I can't tell that, having fired both.
It is expensive and there are nice options that are cheaper. FN makes a comparable gun in the US so it does not have the magazine capacity restriction.
It is also a bit about bragging rights. No matter what shotgun someone tells me they have, the eyes go wide when I reply that I have an M4. ;-)
I think I bought mine for around $1300.