Does anyone have or handled one of these?  How is the fit and finish?  Are they tight?

Finally, since the pin holes are drilled with the upper and lower fit together, is there a problem when swapping uppers and lowers with standard mil spec stuff?  I know you wouldn't normally want to do this, but in a pinch, does it work?

-Red-

this does not answer all of your questions, but...

I got a LB upper and mated it to a Colt lower.  The fit is very tight.  In fact so tight I need a punch to get the takedown and pivot pin out.  I have very good accuracy with this rifle, but it also has different bbl, sight, and toys than my first 2, so i'm comparing apples to oranges.

I hear good things about LB, but be aware your fit will most likely be really tight on another lower.  I threw the LB upper on my BM lower to see if it would fit.  It does and is not as tight as the Colt lower.

LB upper/lower matched sets are very tight (Les Baer designed a machine to machine them to fit  together.  They are a pretty good deal for the price too (as opposed to his overpriced rifles.)

I've seen/handled them but I don't own any (my Ar's aren't that accurate that they need the extra fitting help.)

Get the Rock River matched upper and lower. They are just as good, but will save you some coin. As long as the upper and lower are within spec. paying extra for so called extra accuracy is hype.