I've had some time on the minigen HD. It's performance is comparable to the SNES version from Gamerztek with these differences....
1) There is some sort of weird graphical distortion on movement. It's something that is difficult to unsee, like some sort of dithering. I'll try to post a video showing that later. It shows up especially around the stars that surround the player
2) The included 6 button controllers on the Minigen HD are closer to the original product, than the SNES version and are "good enough" for NHL94, but I'd still encourage folks to bring their own in case they were finicky. For some reason, the cables are fairly short, in contrast to the 10 foot cables on the SNES clones, which are really nice.
Given the choice between composite on an HD screen from an original console, or HD from the clone, I'd go with the clone. The lag was not an issue for me to pull off dekes, one timers, etc. While it's not perfect, it's certainly playable, and would be an improvement over standard systems not attached to a CRT.
In both the SNES and Genesis clones from Gamerztek, there seems to be an audio level issue, as in it's really loud and can easily distort, so you have to keep the TV audio down to compensate.