I had a crap UTG MP5 SD2 that I upgraded with a custom railed SD handguard. Then found and upgraded to the B&T CA body and front end. Decided I didn't like the SD look anymore so I ended up converting it to an MP5A2 then to an MP5A4 with true 3 round burst via the ACSU.
Thus the FrankenMP5 was born with CA, TM, UTG parts and Modify internals. Actually, add WE as I have the WE PDW flash hider on her when I take the tracer unit off. :P