I live in Brazil, and they're not actually made by Tectoy. All the Master System and Mega Drive units that are sold here nowadays are basically the same ones which Atgames (that Chinese company) sells all over the world. Tectoy just imports them and sells them with their brand. Of course, they are licensed by SEGA, but they are nothing like the original hardware. They're basically just an emulator in a chip that connects to your TV in a fancy plastic case. They have some built-in games (with some very questionable choices), and that's it. They don't have cartridge slots and are basically emulators. Tectoy doesn't sell the original hardware (regardless if it's refurbished or not) for more than 10 years.
About the games, I think it's very unlikely we'll see Master System games on Steam. Well, there are a lot of emulators for PCs, anyway. And they're actually way better than those contained in those aftermarket consoles we see nowadays.