These are the converters that were given away for free with import games back in the day by all sorts of stores. There might be more than one manufacturer of the same exact thing, or maybe just a couple of really similar products. I'm pretty sure they are of Asian origin. Maybe it's Barney Mk II since Barney won't fit in a Duo without hacking away a ton of plastic.
This thing is known as the "diving board" for a reason. Your HuCard will stick a mile out of the system. Not bad for a freebie, especially when a PC Engine was $200+ and nobody had yet figured out how to do mods, but massievly pointless these days.
It's not good. It's not official. It has zero charisma. It sucks. I wouldn't pay shipping on the thing. Take it to eBay and roll in the dough.