I have two of these lowers, one from 17 designs and one from NFA, both of which are now closed for business. They have been my primary rifle and primary pistol lowers for 3 years or so. They are great, allowing my pistol to fit in a Vertx Gamut with a 10.5" upper, and my rifle to fit in a typical backpacking backpack with a 16" upper. Compared to a LAW folder these are MUCH lighter and I believe about an inch shorter when folded.
Downsides are that there are multiple set screws which will loosen up with use, I suggest checking them about every 6 months if this is on a rifle you will be using frequently. Also the LOP is increased (not a downside to me) and you have to use their proprietary buffer.
17 designs used to make an A5 buffer, which I have in my rifle lower. Unfortunately Shield Arms does not make one, nor any other weight buffers as far as I know. They really need to now that 17 designs is out of business! Honestly the fact they don't is stopping me from picking up a 3rd lower.