I successfully am using an NES Advantage on RetroPie 4.2.3
I have an NES to USB Adapter plugged into the Raspberry and connect the NES Advantage to the adapter.
I do notice a problem when I boot the Raspberry Pi and the NES Advantage has the SLOW button turned on. The Pi also did not detect the controller the first time when I had the SLOW button turned on. With the SLOW and TURBO buttons turned off the Pi detects the controller without any problem. Then when I load and start playing a game I can turn the SLOW and TURBO buttons on or off without problem. For me, it seems only when the Pi is booting that I cannot have the TURBO and SLOW buttons on or else the controller does not work (I also get stuck on EMULATION STATION LOADING screen when booting up with the SLOW button turned on).
