Re: QD vs Thread On
QDs and thread-on suppressors both need torquing when attaching but you can attach a suppressor to its QD without torquing. Switching a QD suppressor between weapons does not require any tools (but welder's gloves can come in handy).
Compared to the threads on a thread-on suppressor, the OD threads on the QD and the mirroring ID threads on the suppressor are very coarse/robust, meaning it's less fussy about getting started, virtually impossible to cross-thread, and easy to mount on the first try, even if you're in a rush.
In theory, A QD could negatively affect repeatability if it doesn't remount the suppressor to precisely the same location each time because even tiny changes in the suppressor's position will change the bending moment its weight applies to the barrel. However, I've done round-robin test firing of my FN PBR with and without a QD-mounted suppressor and it consistently shoots to the same POI, even after multiple removals/remounts. So if this positioning problem does affect some QD-mounted suppressors, it isn't a universal problem.
QDs aren't free. You don't have to have one for every rifle you want to run the suppressor on, but it definitely makes it handier. However, when you remove the thread-on supressor from the weapon, the threads on the barrel are exposed and vulnerable. When you remove a QD suppressor, the QD remains on the rifle, doubling as a thread protector and a flash hider/muzzle brake. Thread protectors aren't free either.
If you get a right-hand thread-on suppressor, you can't use it on AKs because their muzzle threading is left-handed. QDs are available in either RH or LH threads, so the same QD suppressor can be used on both ARs and AKs.
