I've never tried a beanbag from my Benelli M4 and probably won't unless someone gives me some. But I've fired a few different kinds of standard factory loads including buckshot, birdshot, and slugs from Winchester, Federal, Remington, and a couple of other companies. They've included reduced recoil and full power, and I've mixed them into the magazine in no particular order. What I've been doing mostly is to see if I can get the gun to fail with any combination of anything I might be likely to use. It's not a scientific experiment or a gun test. I think I've fired around 500 rounds from it so far (a guess). No failures.
My M4 is similar to every other shotgun I own in that it patterns differently with different loads and even slightly differently with the same brand and load from different lots. Out to about 10-12 yards with the Federal LE Tactical #00 I usually use, though, it patterns the same as my Benelli M1: one big hole similar to what a slug might do but larger. No difference that I can see.
Slugs shoot accurately from both the M1 and the M4 to 75 yards, which is the longest distance I've tested them for grouping. I have shot slugs out of both offhand at objects (milk jugs, clay pigeons, and thickish twigs) out to 100 yards and the objects go away. It's fun and it seems to impress obervers but I don't think it's an especially useful application of a shotgun.
I've also used the M4 with birdshot at a wobble trap. Let me say as tactfully as I can that I did no worse with it than with most other shotguns. Tom Knapp I'm not.
I'm not much of a partisan for one brand or model shotgun over another. I have a favorite Remington 870, for example, that loves me and I respond with similar affection. I've seen more than a few shooters run an 870 much faster than I can or ever could. Those guys be good. They are better than I am. I, though, with either of the Benellis (M1 or M4) can equal or beat their speed a little. That's no great achievement because I think anyone can do it with these Benellis. I also think those 870 shooters could whip me if they were shooting the Benellis instead of their 870s. The quality is in the shooter, not the guns. I mention it, though, because I think a second tier shooter can equal the usable speed of someone in the first tier with faster hardware. Maybe I'm wrong though, and I don't know if it matters anyway. Focused intensity is what prevails, I think.
One thing I very much like about the M4 (and the M1 too) is that its loading is more efficient than any other shotgun I've used in slug select drills and after the magazine is depleted. Even if the magazine is loaded with shotshells a slug can be popped into the ejection port and chambered without discarding a round from the magazine. I've learned that when the magazine on a Benelli is depleted it's much faster to ignore the magazine and simply load the ejection port and fire a round at a time. I know it doesn't sound right but it is, at least for me. I'll replenish the magazine at leisure but not while running the gun.
My sense of the M4 is that it might live up to its advertising by being better able than my M1 to withstand harsh conditions. It is built like a tank. It's heavier than my M1, though, and therefore not as much like a magic wand. That's not to say that the M4 is ungainly: it isn't, only not so elegant as the M1.
People who have shot both my M1 and my M4 say that the perceived recoil on the M4 is slightly stouter with the same ammunition. I try to feel the difference but I can't. They seem similar to me. I know, though, that when I'm deeply involved in shooting I tend to blank out such sensations and it takes an awful lot to register on me.
In your line of work I suspect that the M4 is a good choice.
Benelli USA discontinued import of its own two-round extended magazine tubes a year or more ago. Some are still floating around for sale. eBay sellers used to offer them until a couple of months ago when eBay policy prohibited sale of such things. They might still be available through sites like Gunbroker though. The Benelli part screws onto the existing tube and extends it. I know of two aftermarket full length tubes. I haven't seen either so I can't speak to their quality. The aftermarket parts are longer and replace the existing tube.
For the bolt hold open release button, look at the photo in the message above. It's the button below and towards the front of the ejection port. That's standard Benelli, on the M1, M4, and other Benelli semi-autos.
