So I got a Gateway, checked and it's a genuine one.
I used Drenn's ROPLoader to install the firmware hack. That seemingly went fine. But then, I place a homebrew Launcher.dat on my Gateway (the red cart), go to the DS profile as instructed, and it halts for a short while, then goes "software encountered a problem, your console will reboot".
I tried both Pong and the RAM dumper, same result.
My 3DS is running 4.5.0-10E.
Did I forget something essential along the way? Or do I need to tweak the exploit to work with an European firmware?
Well, nevermind. I feel dumb now. Didn't notice the part where Launcher.dat is supposed to go on the big SD, not in the red cart.