I had a different experience with these. A couple of years ago, I bought one of their manifold sets to try out in hopes of finding a relatively cheap way of replacing all of my remaining Blue Steel valves (which I don't care for). The DGX valves worked well, but I had an issue after trying to change the handwheels. When reinstalling the handwheel nut, the valve stems snapped at the base of the threads. This happened on both valves (I stopped before trying the isolator) and didn't appear to be related to over-tightening, as I only used a thumb and forefinger on the driver.
DGX promptly sent me replacement valve stems, enough to replace all of the valve stems plus a couple of extras if memory serves, but I had the same issue when reinstalling these, as well. I only got through two of them before relegating the whole thing to the junk pile. To be fair, DGX did try to resolve the issue, but I never followed up with them further. I wouldn't hesitate to buy DGX products (and have since this episode), but these valves weren't for me. With all of that said, my experience is definitely in the minority - there are plenty of users here who use DGX valves all the time with no issue.