You'll need to get a convertor for your TG-16.
Well, to your surprise, PC Engine/TG16 convertor is hard to find and you'll have to pay over $70 for that shit.
I sold mine to Master Terry Bogard for $30 earlier this year.
The reason I sold it so cheap is because I have JPN PC Engine.
Anyway, you have to think about it. If you get a new TG-16, it'll cost you $50 plus convertor (over $70). If you get an used one ($30, maybe?), it'll cost you around $100 - $120 still. Plus, numbers of players have reported that their TG-16 or Duo stop working properly (or can't play import game no more) after a period of time. Sounds like 4-in-1 Pro Action Replay cart will fuck up Saturn cart slot.
My suggestions are:
1) if you want to play US games ONLY, get US console. Keep in mind that a lot of good games were staying in Japan.
2) if you want to play import hucard game and you dont' care about budget, get Japanese Coregrafx, Supergrafx, PC Engine Duo (best choice because you can play both hucard and CD/SCD/ACD games ) or PCE Shuttle.
3) if your budget is tight and still want to play import hucard game, get US TG-16 plus convertor.
Just my $0.02......