Quoted:
Both my kits arrived today in great shape.
I noticed the mid-length kit has a SA bolt carrier, while the carbine has a FA bolt carrier. Would there be any special reason for this? Or are they just using what they can get?
My Neighbor is also interested in one if I don't keep both kits. Is there any reason to favor the middy over the carbine or vice versa?
I noticed this too (see my above post). There are some other subtle differences (different hand-guard retaining cap (triangular vs. round)) too but all in all they are the same quality as the carbine.
Middy vs Carbine is a long standing debate. If you want classic carbine looks, and a small weight savings, keep the carbine. If you want the ability to have longer hand-guards and thus more rail space, as well as an arguably more reliable gas system, go with the middy. Obviously just my two cents, but I've owned plenty of different rifles, and all I have kept are they middys.