As a long-time 8bitdo user and fan I have little doubt this thing will be amazing as a controller.
Having said that, as an N64 controller it very much falls short. Have you ever played Quake with an N64 controller? The experience is pretty great since you can use the digpad under your left thumb for movement and the analog stick (preferably inverted) for looking around. L and Z are readily available for running and shooting, while A makes for an acceptable jump button, leaving you with B, C and R for extra actions.
That's just one example of a layout to that just won't work with this controller (or any other I could find).
Here's hoping that at some point will produce a Dual-Stick layout with switchable assignment for all three axis. Heck, if people are going through the trouble of producing molds for N64 controllers I can't see why we can't get at least ONE with two plugs, so you can assign axis on both controller port 1 and 2 to play dual stick-enabled games like GoldenEye or Turok.