I have a Cohaire SBR with all HK parts that was built by another forum member. It is an extremely fun toy - like a squirt gun that runs like a raped ape. I have a BT mount and a T1, but like it with irons (Ashley trit dot up front / drilled out the largest rear aperture a bit more too). It has an offset SF light / handguard combo, and a 3 lug (waiting for my Octane now). I have also decided I like the funky Choate folder b/c it is very compact and stable. However the fixed stock is the most comfy to shoot with.
It is iconic - like 1911s and Hi-Powers. However, it isn't something I would have paid money to set up; but in this case it was a way for each of us to move through trades that were otherwise not moving. It is a fun toy but it isn't the same as a rifle caliber SBR.