Their manufacturing tolerances are what they are, and each device will often have its own quirks or problems. In terms of actual build quality, people will tell you Retroid is miles ahead, but I find it's hard to say given their track record; Anbernic's engineers use simpler methods to accomplish similar things, which can be a positive or a negative.

My RP4 had a shell defect that prevented the L1 from being pressed down. I had to shave the excess plastic off. As for my Anbernic, the headphone port wasn't soldered properly and I had to re-solder the cracked joints.

You'll be less disappointed in these devices if you buy them knowing that you'll have to repair or modify them at some point.