I average 10-12 seconds on 3x3 and here is my opinion: I highly recommend this on the maglev version of the rs3m. The difference isn't night and day, you will just lock up less with the core magnets. I main the gan 11 m pro/duo (i switch between them) and I dont really like the rs3m by comparison. But this upgrade makes solving on it much more enjoyable. The puzzle is still a bit too heavy for my turning style but that's just personal preferance. I'm not sure but I think this is more or less the same as the CH core magnet kit just half the price!! (Side note: one of the corner stalks had excess glue on the magnet which i sanded down to make sure it fit in the cube properly.)

I want to first start off by saying that when I opened the package I immediately saw that one of the parts of the magnetic core was broken. I didn’t really think too much about it, but when I was gluing them in, it took very long because they kept moving around. Once they dried a bit, I put it back together, and also installed the MagLev kit that I got. Overall, it’s worth it but if it comes broken, it’s pretty hard to fix.

Just finished install. Fair amount of glue but seems sturdy everything fit well. No complaints so far. Bought a mag lev kit as well so (fingers crossed). Hope I don’t mess this up.

it broke on the second day

Maru Core Magnetic DIY Kit for RS3 M 2020

I liked the RS3M 2021, but I wanted a stronger magnetic feel. Previously I'd used the additional magnets, but I felt that made the cube feel heavy and the weight distribution felt off. So I removed the extra magnets and installed this kit. If you have the kind of super/krazy glue that applies with a brush, it's very easy to install this. The only snag I hit was due to one of the corner pieces of my RS3M had a small piece of plastic stuck in the hole that the magnets sit in. Because I couldn't pry the plastic piece out, I just trimmed the magnet piece. The cube now feels stable and has a better weight distribution. Definitely worth the money.

This was incredibly easy to install, just a couple dots of super glue and drop the pieces into place. The corners fit very snug and with a little twist will settle down to a uniform height. This might just be my brain tricking me, but it does feel like it weighs a fair bit more even though the kit itself is quite light, but this also doesn't have any negative effect on my turning.
Overall, this was a really fun and easy mod to install and feels good to solve with. It's not a massive difference but it does feel very stable and snappy