what is the difference between the R4 and M3 Real with GBA port

I know the R4 cant play GBA games since its a slot 1 device. Does the R4 and the M3 slot 1 device play roms and everything the same? what are the advantages and disadvantages?im also wondering if the M3 slot 2 device runs GBA games at full speed?

i hope to buy one of these very soon, so information on said topic would be great.

thanks