I got the four port adapter working finally yesterday on Retropie using Debian Jessie image (not the standard wheezy RetroPie image) and building the ToadKing driver on Github. Need to get it to run at start up.
Configuring the controller in Emulation Station seems to be problematic at best (even without the usual bugs in assigning buttons when connecting controllers) because of the uniqueness of the controller in comparison with others. It would need to be configured manually. Haven’t sorted that out yet and I’m not convinced it’s the best controller for some systems.