Only advice I can offer is stay away from any older MP5 clones you may come across that are marked as Special Weapons, Coharie Arms or Bobcat Weapons. Also, Top Notch and Black Market were companies that just sold parts. Those guns, plus likely a few others that I'm unaware of, all had the infamous Todd Bailey associated with them and their quality is pretty spotty. Definitely a buyer beware situation. A quick google search will provide more bad news about Todd Bailey that you'd ever want to know.
I have never spent as much money trying to get a gun running right as I did with the Special Weapons MP5 clone I owned. I poured a ton of money in it for parts and gunsmithing as well as a shitload of ammo burned up for testing. I never could get that gun to run right and sold it for a big loss to a buyer who knew its ills but planned to have one of his HK auto-sears installed in it after having it rebuilt by a good HK smith. He eventually had to replace the receiver to get the gun right.
By around 2012 Todd Bailey's reign of terror ceased so newer MP5 clones should be much better although I have no direct experience them. I do hear the MKE clones are supposed to be better but I'd never do another HK clone again. For me a real deal HK is the only way to go as it'd be cheaper in the long run plus you have a gun with some real value.