The only thing that has kept me from buying one is the gas piston. It is a pain to clean. Neglect it and you will regret it. I am used to a long recoil action gun that can, if need be, somewhat neglected and still be reliable.
The gas piston on the Beretta is an education in "do not neglect" or you will suffer.
I own an A390, made in Italy in the 90's. Wood furniture. I recently bought one of the AL390s from Bass Pro to use for hunting. The AL390 is marked "Made in USA" on both sides of the receiver. The barrel is marked "Made in Italy". It has the humpback receiver, the A390 has the rounded one.
My experience with the gas piston has been nothing like RetiredLawman's. These are the most reliable auto loading shotguns I have ever used. I have gone as much as ~750 rounds without cleaning on the A390, because I use it for clays, and there have been a couple of times that I just didn't have time between sessions.
I drop the piston in a jar of Ed's Red for 30 or so minutes and brush off the carbon with a brass brush. Big deal.
These are not 3901s, technically, but actually they are. I expect the 3901 sports a better finish. All parts interchange as do most parts for the 391s.
In my opinion (whatever that's worth), this is the best value available anywhere for a quality auto loading shotgun.
I have shot many thousands of rounds through these guns (mostly through the A390), and have never had a failure of any kind. Ever.