I have and LR-300 11.5 SBR. So far I love it. I already had the lower registered and I found the kit on Gunsamerica.com. So it was just a matter of swapping uppers for me. I think they are pretty rare though.
If you order from Allan make sure you have all the SBR paperwork completed and approved.
But I think you might find a used one sooner, hard to say, maybe I got lucky (I think the wait is 10 months to a year, or longer refer to Master_Blaster's excellent post) .
My observations with the few rounds I've shot so far.
Have not experienced any malfunctions.
Virtually no muzzle rize and little recoil compared to my old upper.
The phantom FH is very effective on the short barrel.
Very accurate.
Although the gas is still fed back into the bolt, the gun still runs cleaner because the gas tube doesn't discharge into the upper receiver.
Mine has feed ramp cuts like the colt M4s.
Fun, Fun, Fun to shoot.
Things I don't like.
It is too heavy with the steel ZM folding stock/battering ram.
I like the adjustability of the collapsible stock (I've solved both problems by just putting on a standard stock with a plug, I'm currently looking/saving for an nice lightweight folding stock that I can get to work).
To accomidate the spring and larger tube above the receiver the ZM upper had to be raised a little bit. This also raises the sights (It's always nice to have the sights as close to the muzzle as possible). So far it hasn't been a huge issue for me but something to note.
It has a nice forward assist that I don't think it needs.
Some non standard Parts that might be hard to find.
So far I really love this gun. It looks cool, it's accurate, reliable, unique, has a practicle wieght (not too heavy, always wish things are lighter, but it's definately managable) and gets a lot of attention at the range. Even the AK guys like it [:)].
here it is with ZM folding stock.
[img]http://www.hunt101.com/img/047928.jpg[/img]
here it is with the collapsible stock,spacer, and Eotech.
[img]http://www.hunt101.com/img/049899.jpg[/img]