When I bought my L21ZSM (used) about 7 or so years ago, I immediately went on eBay and got a brand new side bagger kit for it. And there the kit sits on my shelf in the garage the last 7 years or so. Still brand new. Never used.
The Snapper is my goto machine for bagging as I only bag leaves in the fall after mulching them. The "HiVac" feature of the Snapper is superior to LawnBoy in my opinion. I also have the Snapper HiVac super lift blade that helps. It even picks up pine needles. Amazing. But if I only had my Lawnboy, I'd definitely bag the leaves with it in the fall. Unfortunately, the Snapper is a commercial industrial model with a heavy steel deck, steel wheels, and a Wisconsin Robin commercial engine, so it will last longer than me.
I think next fall, just for poops and giggles, I'll at least hook up that brand new side bagging kit to the LawnBoy just to say I used it.
Honestly, I just like mulching. But I have a wooded lot and in the fall even with a lot of mulching, I have to bag the remains of the millions of leaves I have mulched as best I can. They still need cleanup after mulching. Mulching just makes it easy to bag with less trips to the firepit to empty the bag.