I saw this in a local shop. It's not cheap https://imgur.com/gallery/uvxs9oJ...

I've seen a bunch of these carts in the last few years. I think they were older flash carts that were used with Famicom Writer hardware? I have a couple of these in my own collection, but I'm not entirely sure about the label data on this particular sample? I would estimate $25-35 from what I have seen, this one is $100?

Yeah they basically want $100 for it.  It's a retail used-goods store so a lot of the time they want really high prices, but once in a while you can find something interesting for a reasonable price.  

 

Nintendo and Mitsubishi Electric did partner to make some games but that was before the Famicom was released.

It's cart with eproms, can copy games onto it. This was obviously made with Japanese market in mind, I have several for the Taiwanese market, same idea but different manufacturers. The switch changes mirroring, I believe

I had one of these. I think it was called a famiwriter cartridge and that the switch was for switching the mirroring.

Very interesting, thanks for the answers everyone! I think at that price I'll leave it at the store....