My friend has a really low-end single core A4-4020 APU, 8 GBs of DDR3-1333, and installing this mod makes it so he only gets like 1-4 FPS in game, without it he can reach 30+, is this a known issue?

"installing this mod"

I'm really curious, if it really doesn't happen without this mod. You might want to fiddle with the config flags in foamfix.cfg, disabling them one at a time until something holds.

This could be related to the sprite animation optimization not being liked by AMD drivers, which has been worked around by blocking the optimization on AMD cards.