I think it all boils down to whether you would prefer a gas gun to an inertia gun.
I have a M1 Super 90 which I got when CDNN was closing out the last HK-stamped Benelli shotguns. Around here you can find M1S90s for $750-850 so I don't think they are out of your price range.
Both gas and inertia guns have their advantages and disadvantages.
Gas guns are more reliable when you start adding bells and whistles to your gun. When you start adding sidesaddles and Surefires to an inertia-operated gun, you change the inertia of the gun (inertia is directly proportional to mass). Gas guns don't care about the mass of the gun, you just gotta have enough gas to cycle the action.
If you buy an inertia-operated gun, you MAY experience reliability problems when using light (i.e., field or tactical) loads with a fully-loaded TacStar sidesaddle and Surefire Responder weapon-mounted light. My M1S90 has a Responder but no sidesaddle and it has never choked with Federal tactical loads or light field loads. Even if you do decide on an inertia gun and all the bells and whistles, Benelli and Wolff Gunsprings offer a special recoil spring that fixes the problem. Or you could use standard 2.75" loads....
Inertia guns also have less parts than gas guns. Less parts, more reliability.
However, gas guns are harder to maintain. Cleaning is more difficult and more important. I once left my Benelli sit for an entire year without cleaning inside the receiver, using it through the normal competition season. I would only swab out the barrel, keeping the bore nice and shiny. I opened it up and barely had to do any cleaning whatsoever -- inertia guns don't build up fouling like the gas guns. Thus, gas guns can start giving you reliability problems if you don't keep them clean, especially after heavy usage.
Therefore, to keep your shotgun reliable:
1. Don't load the inertia gun down with too many accessories.
2. Keep the gas gun clean.
If you really want an inertia semi-auto, why not the Beretta 1201FP? It uses the exact same action as the Benelli, all for dealer price of around $380-420. Control placement is a bit different and you lose one round of capacity but hey you save $300-400 and it's not looking that bad. The 1201FP, while sometimes hard to find, is an excellent gun -- my best buddy uses one and not only that, John Farnam uses one as his personal defense shotgun.
HTH,
Justin
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Justin T. Huang, Esq.
late of Kennett Square, Pennsylvania