DO NOT BRING THE TM M4'S FLAWS OUTSIDE OF THEIR M4 LINE.
Goddamnit. TM's MP5's are amazing, they have AMAZING hop-up designs... TM is amazing all around. You're paying for engineering, research and amazingly machined pieces.
Everything will fit together like it's supposed to, every upgrade you put into it will work flawlessly... EVERYTHING WILL BE GOOD IF YOU GO FOR THE TM.