Pretty disappointed with the emulation on this device wondering if I can replace the motherboard with a pi zero or something. Or may end up getting a backlit GBA on ebay or RS97.
I mainly just want to play pokemon GBA and fire emblem
You could certainly try putting a Pi Zero in the shell. I haven't heard of a kit or anything like that for you to use, but there might be something like that out there.
The RS-97 seems to do very well with GBA emulation, once CFW is installed. One thing to note is that some newer units, labeled 1.0S under the battery cover, have incompatibilities with CFW that haven't been fixed just yet. (The preferred GBA emulator, regba, doesn't run, which leaves you with gpsp.) Also, the RTC stops when the unit is powered down.