I would second the Duo-R. The Duo-R, along with the other Duo systems, has the ability to play Super CD games right out of the box, and you don't have to futz around with System Cards unless you want to play Arcade CD games. The Duo-R is also very reliable, especially compared to the original TG-CD/PCE CD setup.
You also won't be able to play TG-16 HuCards on any Japanese system unless you mod it, but I wouldn't worry about that since the PC Engine equivalents of TG-16 games are usually cheaper. That, and most of the TG-16 exclusives suck so you won't be missing out on much.