the better inertia semi auto shotguns are retay masai mara and gordion. they are copy of benelli shotguns, but without the problems and recoil of the benelli shotguns. and less expensive too. if you want a close to perfect benelli, they are it.
some of the best gas operated semi auto shotguns are fabarm xlr5 velocity ar. they cost twice the price of a benelli or beretta. made in italy. they are work of arts. and they shoot and handle like a dream. if you want to spoil yourself.
my personal semi auto is a 12 gauge beretta a400 extreme unico camo optifade with 30 in barrel. it is built like a tank, a dream to shoot even with heavy loads. recoil is much easier to manage than a benelli. i had a super black eagle 2 and it kicked like a mule. it is gas operated, easy to maintain and it is heavier than a benelli. over 8 pounds. the gas system and weight tame the recoil. you can shoot 2.75 shotshells all day long.
if you want a very good semi auto with 21 or 24 barrel, check the 1301 series of beretta shotguns. my favorite is the 1301 comp pro with 24 barrel. but yes they are expensive.