I got a chance to try out one of these controllers with the original Super Smash Bros – serendipitously right before my interview with its creator, Masahiro Sakurai – and it seemed to work swimmingly. I didn't notice any significant input latency, and was able to perform smash attacks without any trouble (as Samus, obviously).
I doubt I spent more than five minutes with it, so I can't speak to longterm concerns like connectivity issues or battery life, but the initial impression was definitely a positive one. The build quality felt good, though not as high as official Nintendo controllers. The analog stick in particular felt like it didn't have as much weight or resistance to it as an official pad – more or less how you would expect a third-party controller to feel.
Connection is achieved via a receiver plugged into the console's controller ports. The receiver has a connection button and a slot for a memory card or Rumble Pak. Obviously you won't be feeling any of those rumbles from across your living room, but at least the option is there for any games that require the Rumble function (like finding secrets in Ocarina of Time, etc).
The Wireless Hypermode N64 controller is slated to arrive this summer for $30. A Genesis version and an NES / SNES hybrid version are panned for this fall at the same price.%Gallery-191540%