I bought an mClassic a few days ago. It's advertised as a "graphics card for consoles", and it's an adapter that adds anti aliasing and upscales, amongst other things. With only a little bit of usage under my belt, I can't say I'm blown away, but it's definitely a neat concept with noticeable improvements.
I bought it to fake a "Switch pro", but I've heard it's even better for older consoles. I'm thinking it might actually be better for my old 360/PS3 games, and possibly Dreamcast/GameCube/PS2/Xbox with the appropriate adapters!
Just as an example of what it can do, I took a screenshot of a character I have (one of several!) on PSO2 on a regular Xbox One. The mClassic screenshot is on the right, and it's definitely an improvement!
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Some games it's better than others. It really seems to help with the Switch more than the Xbox One or PS4 thanks to the added antialiasing and such. Not my video, but Animal Crossing, for example, looks pretty nice with the mClassic:
Is it worth $100? Probably not, but if you have the cash and want to make your console games look a little prettier, it might be worth a look. It's supposed to upscale Blu Rays to 4k as well, although I haven't tried that yet!