There are some known issues with the patch, as described
here, but all are minor and none of them are game breaking. For example, sometimes a gift box's sprite is replaced by a poison status sprite. But the present still works.
However, the one issue that may be a bit of a problem is that occasionally the main text dialog slows down (which may or may not be lag). It probably has something to do with the current CPU load while the patch's sprite welding algorithm is running. (since the GBA can only have 128 sprites on screen, letters have to be welded together in sprites rather than one character per sprite, which was allowable in Japanese for obvious reasons) Mato optimized the sprite welding algorithm as best as he could, but this issue still appears every now and then. Avoiding this lag could be optimized in a TAS, but from the issues in that list, this is really the only one that should be worried about.
Besides, if a game breaking glitch is discovered, it shouldn't be too difficult to check the Japanese ROM to see if the glitch exists there too.