I have been reading Chinese forums and this is what people consistently reported. It seems both Taiwan and Japanese made Kingston 1 GB micro SD cards will work with R4 most of the time. However, for some picky ROMs (like Castlevania PoR), the chance of freezing is lower on the Japanese made micro SD. A simple test is to run Castlevania PoR and spam starts in game. If it doesn't freeze, then you are good to go.
One poster reported that the Taiwan and Japanese made Kingston micro SD cards apparently use different manufacturing processes. The Japanese card uses one IC chip of 1 GB whereas the Taiwanese card uses two IC chips of 512 MB each. How valid is this claim is beyond me; I am still waiting for my card to arrive. >_<
EDIT: Fixed 512 MB (instead of 512 GB) and some spellings.