I've bought the MM3 from Eurasia. IIRC they do work in all PS1 systems, you just wire the pins to different places depending on the revision of the system. I've got an OG launch model and a PSOne that have the same chip. It's super easy to install in the regular PS1 systems, you need some decent skills to put it into a PSOne though with the super tiny solder points. Voultar's mod shop sells premodded PSOne pcbs if that's the model you want and you're feeling lazy.