Is this really an 'upgrade' though... more of a sidegrade... It's just the same features in a miniture case...
Whereas going form SD2SNES up to the SD2SNES Pro/FXPak Pro was a major jump.
AFAIK the FXPAK PRO doesn't currently have any additional features over the original SD2SNES, so its not really what I would consider a '
major jump'. Sure the hardware is improved and could theoretically support things like the Super Game Boy in future, but those extra features could be a long way off (Remember how many years it took for the SD2SNES to gain Super FX and SA-1 support) [
<EDIT>Just one week after this post and Super Game Boy supports randomly appears for both the original and Pro!] Based on the current features, the SD2SNES -> FX PAK PRO is more of what I would consider to be a sidegrade.
IMO flash carts that actually are major upgrades are things like:-
EverDrive GB -> EverDrive GB X7
EverDrive N8 -> EverDrive N8 PRO
Mega EverDrive X7 -> Mega EverDrive PRO
Sidegrades are things like:-
Super EverDrive v2 -> Super EverDrive X5
EverDrive 64 v3 -> EverDrive 64 X7
EverDrive GBA X5 -> EverDrive GBA X5 Mini
Sure the newer carts are likely to receive support for much longer and could receive new features in future, so if you are buying your first flash cart you may as well buy the new versions. However if you already own one of these carts and are trying to decide if you should 'upgrade', then you can only really compare them based purely on the current feature set of each cart.