I've had a good number of issues with the 6 or Benchmades I've owned, including poor edge grinds, uncentered blades, blades with vertical play, liners shifting within the noryl gtx handles (on a doug ritter grip), and completely unfinished, rough tang grinds (on a custom barrage, no less. They literally send you a video describing the process of finishing the blade tang, yet neglected to do it on mine). I've had duds from a lot of major companies, like Spyderco/Zero Tolerance/Microtech/Cold Steel, but Benchmade has definitely been the worst high end company for me in terms of QC. I won't buy another one unless someone proves to me that the individual knife in question is perfect.
The main issue for me is that Benchmade doesn't seem to regard these as issues. I sent an adamas and a custom barrage back to them with vertical play, told them what the issue was and what caused it, had them confirm that via email, then got the knives back with both vertical play and the pivot tension adjusted wrong on both blades (way too tight on the barrage and way too loose on the adamas). The barrage was also missing the safety switch when it got back. The knives were literally returned back to me worse than when I sent them in.