I believe they're only used for games needing 1M or 4M RAM cart games. Most of the 1M games will be SNK games, and most of the 4M games will be Capcom games. (Although you can keep the switch in 4M setting because that'll still work with most 1M games).
Expansion RAM carts like the above won't show up in the main menu. I have the official Sega ones (1MB and 4MB), and they both don't show up on the main menu. Only way to know that they work is to actually play a game that uses them.
But to use this cart, you'll need either:
1. A Japanese Saturn - because all the games requiring the this cart are Japanese games (minus US version of Marvel Super Heroes, maybe... someone can correct me)
2. A Saturn with a region-switch installed.
3. A Saturn that plays CDRs, so you can change the Japanese region code of the game to US then burn that to a CDR, which will allow it to boot up on your US saturn.
Now all this stuff I said is assuming that I got the cart correct. I don't have it myself, but I just recall seeing this cart somewhere on the web.