If you're looking in the $150-is range, I just put a Parallax Tactical FFSSR Lightweight Series, M-LOK in 13" on order, and it was about $155 + a few dollars for shipping. At the $200 range there are a ton of options, just think about what exactly you're looking for. I specifically wanted a very light 13 or 15" rail with a small diameter and that has a solid and quick mounting method with screws into a beefed up barrel nut (or similar). Most importantly I wanted something that's easy to take off and reinstall with minimal realignment headache (think advantage of the Aero M4e1). I also have a troy alpha rail on a SBR, and while it hasn't budged on me yet under gentle range use, having to install it on my kitchen granite countertop while turning each screw a teeny bit at a time while alternating screws really irritates me. It never seems to set up the same each time it gets reinstalled. I admit its not a huge deal and not worth taking off and replacing, but it just aggravates me. I have a low profile adjustable gas block under the rail that I want to get to for cleaning from time to time. Otherwise it does seem to be a decent rail. I think the "uses the standard barrel nut" argument is overhyped if you are barreling the receiver yourself. Its great if installing the rail on an already built upper and don't want to touch the barrel nut, but when building from the ground up I think there are better options. The Parallax barrel nut goes on and off with a 1.5" (I think) crow's foot. I really like the advantages of the Aero M4e1 upper when it comes to taking the rail off and reinstalling, but once again I opted for the standard upper rather than the Aero. I'm not crazy about how fat the Aero rail is. Plus, one can find 2 - 3 built but un-barreled uppers (even blems from Aero) for about the price of one of their un-barreled enhanced upper receivers.