If I need a weapon that rock and rolls, we're way past the point where the law will matter. An auto seer takes 8 seconds to drop into a Colt AR-15 that already has the spring kit, and as long as the seer isn't in the receiver, there is nothing illegal about it.
Unless they've changed the rules in the last few years, owning a "Legal" Pre-81 Drop In Auto Sear AND a Title 1 (semi auto) AR are enough to arrest you with an "intent to manufacture" or "posession of an unregistered machine gun" charge, even without the rest of the FA parts. Even having one FA specific part had gotten folks into trouble, and they are useless unless you have all of them. The post '81 ones have had to be registered as machine guns prior to 5-19-86 to be legal.
When I started playing with Title 2 stuff about 25 years ago, (I had a registered Receiver AR, and M2 Carbine and a suppressor) even the FA bolt carrier by itself was considered by most folks to be a no no on semis.
Most of the bolt carriers used in semis had the auto sear trip surface either partially or completely milled off.
IIRC, only Colt, in an effort to foil attempts at making them full auto, put the large hammer/trigger pins and auto sear block in their lowers of that era too.
Spring kit? The only spring that is different on a FA AR vs. it's semi auto counterpart is the auto sear spring, which is not needed with a DIAS, since they typically have them built in and don't use the original M-16 auto sear or spring. The assembly sits in the cavity behind the trigger group, functioning exactly the same way as the M-16 AS and Spring, without the holes in the receiver.
You can put a DIAS in a semi AR and it will not do anything unless you have
all of the other, full auto specific, parts installed. Trigger, hammer, disconnector, selector and bolt carrier are all different from their semi auto brethren, although most ARs seem to have the FA BC nowadays.
A relative of the DIAS is the "lightning link", which will turn any AR with the proper BC and no receiver block into a full auto (only) machine with no extra parts. You need the BC from a pre "blue label" Colt for them to work, as the auto sear trip ledge was only milled back about an inch on those, and would trip the LL. If you use a FA carrier with these, you risk firing out of battery or it simply not firing at all, as the hammer will most likely just follow the BC as it goes forward. It might even impede the BC from going into battery at all. If you use a BC with the entire sear trip ledge milled off, it simply won't trip it.
The Title 2 rules get complicated real fast, and many states have their own laws WRT to possessing them, so anyone interested in legally owning them needs to do some homework. FL is pretty easy. Having done both, legally owning Title 2 stuff in FL is easier than owning a pistol (legally) in NY state.
All that said, FA is a ton of fun to play with (my old neighbor, who got me into the Title 2 stuff was a Class 3, and had 29 registered FAs that we'd go play with.......often
), but in a SHTF scenario, where resupply is not likely, FA is the LAST thing you're gonna need.