Only spent a few hours on this on my chinese handheld and already in love. Still suck to perform all the tricks this has to offer and the ergonomics of my R35S are probably way worse than of the GBA, but man it's a joy to use this.
I use a R36 Max Clone.
Had to disable the save state and load state hotkeys to in order to have some of the FMS tricks work properly.
While in game, if you hold Select+X you should be able to set the bindings of the emulators hotkeys.
I couldn't figure out how to make a control blank, so I just set the save/load macro's to the weird middle ball button thingy that the max has.