Steve - All my 16's are sear guns, and for the most part, I'm very happy with them. I'm a shooter, not a collector; if its in my safe, its going to be shot and its going to be used. With a DIAS gun, you don't have to worry about beating the hell out of an expensive registered receiver, or getting it scratched, dinged, or marked. Other than the DIAS, you can replace everything - and use a post ban receiver. I've dropped guns, tossed them uncased in the back of the car, and I give them a good work out. Don't get me wrong; I don't abuse my guns, but I don't baby them either. With a registered receiver, especially a factory Colt receiver, I wouldn't feel free to treat them like shooters; I'd be more afraid to take them outand put them through their paces. If I had a factory Colt M16 and scratched or dinged the receiver, I'd be pretty fooking upset. With a DIAS in a $100 post ban receiver, its no big deal. Basicly, a DIAS gun is perfect for the guy who is going to really use his guns. There are drawbacks though. First is properly timing them - its not usually a problem, but it does have to be timed specifically for each upper you put on the lower with the DIAS. Next drawback is you can't get a 3rd burst option (not that its difficult to pull a 3rd burst in full, but you can't install a 3rd burst parts). Additionally, with a DIAS, if you get a LMG upper, you can't take advantage of the open bolt set-up. Ciener kits can be more problematic with DIAS also (you can get them to work, but it may take a little more tinkering than a reg rec gun). I remember recently surfing by some guy's site who had a couple RDIAS's for sale at about $3900 each - I can't remember the site, but I'll see if I can find it again. They're out there but $4500 is on the high side. Right now, with the NFA market as slow as it is, I'd think one could be had for $4000 tops. No guarantees, but if you want, I'll check around with some of my contacts and see if I can locate a couple.