I've heard plenty of thoughts on why not to shoot a .22lr out of a standard upper. In my experience, which is simply anecdotal, I haven't had a single issue through thousands of rounds. The chamber should stay clean, as every adapter I've seen has a 223 to 22lr filler that fits in the chamber. The bore may get a little lead fouling, but a few rounds of 223/556 seem to deal with that well enough. I've also heard the adapters can clog the gas tube, but again, a few rounds of 223/556 now and then seem to keep that from happening. The accuracy I had was well within my plinking desires and worked just fine. It was never a benched rifle so I'm not sure how much more a dedicated solution would squeeze out.
Now, I have gone to a dedicated 22lr AR type platform, but that wasn't due to any flaw in the performance of a conversion. I simply rather not have to keep track of which bolt I brought with me and which optic setup I'd like to run. The 223/556 stays that and the M&P 15-22 stays 22lr. I also like to buy firearms and having two is better than one and a conversion kit in my book. If the budget limits you to a conversion kit, I haven't had any issues out of the CMMG. The JAC kits were made hit or miss and the customer service was worse yet.
I would NOT shoot 22lr through a 556 suppressor. It seems to clog a can up real fast and most 556 cans are sealed, making cleaning a bit tough. The chemical cleaners work well but are extremely toxic and hard to dispose in a legal and safe way. It's just not a situation I'd like to mess with. I'd either mess with springs/bolt weight until sub sonics worked, use hearing protection with HV 22lr, or buy a 22 Sparrow suppressor if you really wanted to use one on rimfire.
