The top right button that's cut off is a C everyting else is the same as a standard one the two switches on the bottom control the rumble (on/off) and to use the 4 or 6 button mode if set to 4 button mode Z and C become Face button counterparts of the triggers
The back part is kinda iffy on the real dreamcast controler you can put the cord through easily and it stays there on this it falls out all the time but not really a problem
Ignore the pic of my cousin... it has one open slot for a vmu the other port is taken up by the built in rumble pack but i guess if you opened it you could get it out