I like that it comes unassembled, since that comp would never go on one of my AR barrels shorter than 16". But for $140 that is an excellent price, especially for a .300BLK upper, even if you don't use all of the parts.
I actually happen to like the 8" 9mm upper they have for $140 a lot better. It is definately worth the extra $15 to get it assembled, if you don't know how to do it yourself. But a 9mm blowback is even easier than assembling a 5.56mm or .300BLK as there is no gas tube or gas port to mess with.
Primary Arms is running a sale on all of their AR lowers starting, but the best deals are on Aero Precision Specialty Gen2 lowers, starting at $48. The AP Gen2 lower is IMO the best MILSPEC lower on the market, especially for the price, and if you want something different, like "Don't Tread on Me", or Texas, or "Freedom" or just markings for a M4 or M16A4 retro build, they are all on sale here. I love the tensioning screw, but those set screws that keep springs from flying every where, every time you disassemble it are worth the extra cost. If you want the billet look for $65 and up you can get one of their enhanced lowers.