Here's an argument on how I feel about the RS3M 2020:
It's not actually that great of a cube. I know this is a controversial topic, and you might disagree, but I have many problems with it. First of all, I don't like the plastic. It feels quite thick, unlike the Guhong V4, and although this plastic makes it more durable, it doesn't feel as fast in a sense, and it also makes it heavier.
Second of all, the mechanisms are kind of a pain. I feel like this is the problem I had with GAN cubes: they have a zillion different adjustments. Especially for a beginner, who just has started cubing, the RS3M would be recommended to them, but I don't think they could quite figure out the spring tightening system, as I could barely figure it out myself. I'll just take a spring and screw myself, thank you.
Third of all, the magnets are quite weak. Personally, I like stronger magnets, but the thick plastic of the RS3M was slightly blocking the pull of the magnets. Therefore, I got the magnet add on, where you add extra magnets to the cube. This did help, and I liked the feel of the magnets, but now the cube was much heavier, making it not enjoyable to cube with.
And last of all, the spring noise was really annoying. No matter how much I tweaked it, no matter how much lube I applied to the edges, corners, springs, screws, etc., the cube still made annoying noises. Whenever I turned a specific face, the cube almost made a grinding sound. Now, I hope you can see why I really don't like the RS3M 2020, but I'm hoping the RS3M 2021 is better.
Feel free to share your thoughts on this as well if you agree/disagree.