I bought one like this:
Variant A-B here:
https://www.aliexpress.com/item/1005004672234065.html.
The YouTube channel the video above is on can be fairly helpful if you'd like to see how some of these work.
However, I haven't tried it yet, because I also bought this at the same time:
Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com
https://www.aliexpress.com/item/1005005048083124.html (I'd call this a very helpful upgrade and wouldn't want to be without it)
I initially wanted to go for something like a Lansky system, but I think it only goes down to 14 degrees, but I have a knife that's 12 degrees.
The rest of them seemed too expensive for what seemed to be diminishing returns.
The stones that came with the Ruixin Pro RX009 might not be the best there are, but they've done the job on a few knives so far.
I also bought a digital protractor, because while a phone could do the job with an app, a standalone protractor is a simple tool and better suited for it.