I have a bootleg and an original Puzzle Bobble. The Bootleg has big EPPROM chips on the inside, and no branding on anything. The original is all real chips, and has SNK branded on the board. Both work pretty well, although the sound on the bootleg can be touchy at times (requiring you to reseat it to get it to play right)... other then that they are identical playing and looking on the outside.
-Nick