Yep, been there.
However, it was with the holy grail to some, the Retro Arms AR15 CNC hop unit. I bought two of them and the first shock was their internal finishing which had burs here and there, but easily sorted. They were ever so slightly too long though in four AEG's I tried them in, with the upper never going back on properly (both metal and polymer receivers), other than in a G&G Firehawk.
The Maxx Model M4A-PRO though, hated by Reddit, fits perfectly in every AEG I put one in, but had to change the nozzle in all of them to get the best out of them.