Here's a funny thing. I believe PS2 and GBA were the only devices ever to have both GameShark and Action Replay cheat devices, this actually is even more obvious since the original GS for GBA... is literally the same cartridge as the later AR, makes sense since as said, Datel were always the creators of GameShark, but InterAct released them in NA.
Then when MadCatz took over, they released possibly ONE legit cheat device; the GameShark SP:
Now check out for fun, the original GameShark and the Action Replay version:
Funny you can see that the innards are different despite the same shell.
ALSO, I can tell you first hand that the GameShark SP by MadCatz and Action Replay by Datel are very different.
See, the GameShark SP used far shorter codes (usually only two lines IIRC) compared to the like dozen lines for the same Action Replay codes.
But despite that, each felt they had their own advantages... I just can`t quite remember which, even ignoring the code lengths!
Also wanted to mention, this means we did get the GameCube GameShark in the end, they just changed the branding back to Action Replay to use instead in NA, meaning, it'd have been pretty redundant to release a Datel-created GameShark, when InterAct was near bankruptcy, only for Datel to just release it in NA anyways under its real name.
Only difference in the end is just the slight change in the interface (and maybe code lengths? Not sure how the GBA GameShark by InterAct handled codes, if they were shorter or if they were also like a dozen lines long.