Thanks!
As for MKR, from my research:
Maker (MKR) is a token that gives voting rights to the borrowing system that is used to generate the decentralized stable coin Dai.
So MKR itself isn't stable coin, and it's not meant to be. It's token for another stable coin. Also, if you look at the price you can see it fluctuates way to much to call it stable.
As for BNB, it's purpose doesn't matter. If you can trade it, you can make profit or lose. It's tradeable. Which means it's usable for trading system tests.