Yes, indeed, the BPS 10 is MUCH easier on the shoulder than shooting 3.5" 12 out of a 535. i own a 535 and my best buddy has a BPS10. The weight really helps. But, for duck hunting I shoot 2 3/4" 2 or 3 fast steel. I'm not sure why you'd wanna shoot a 10 at ducks. Fast steel in 2 3/4" does the trick just fine. Perhaps you're pass shootin' them? 2 3/4" or even 3" 12 is SO much easier on the body than 3.5" and I have a limbsaver on the 535. A box of shells out of that thing on geeee would be brutal. I've fired 21 rounds out of my 10 before, a little sore in the shoulder, but nothing to write home about.
I have an H&R 10 gauge, a 9 lb gun, and use it on geese. Snows can be WAY up there on a blue bird day and what with the price of hevishot now days, my 10 has already paid for itself. 10 gauge steel T works better than 3" BB hevishot for me. For one reason, the patterns are over 90 percent in a 30" pattern board at 40 yards, best patterning gun I've ever fired. My 12's best patterns with 3.5" are in the low 80 percent range, good patterns, but don't compare to the 10. I'm not saying the BPS will pattern that well, but I'm betting it'll be better than the best you can get with a 3.5" 12 because not only my experience, bot others I've talked to will corroborate me on this.
But, if you're hunting ducks over decoys like I do, even in the open bay, a 2 3/4" fast steel load is all you'll ever need and they're cheaper. 3" is overkill. My 10 is strictly a snow goose getter. The BPS is my favorite pump, even though i don't have one. The ergos, especially for a lefty, are far superior to anything with a crossbolt safety and not having a shell elevator in the way is the only way to go on a cold morning when you're wearing gloves. However, my Mossbergs shares these features, shoot just as good as any other 12, and are lighter as they have aluminium receivers. That's a big bonus when the gun has to come up fast on those early morning, low flying teal. Even the BPS 12 is heavier than the Mossberg. The 10 is an even bigger lump of steel.