Magnets change cubes, I find.
My Valk M (Custom Magnets): It kept its personality, roughly... if anything it became more exaggerated, more stable and a bit slower.
My Gans AIR UM: The cube finally feels... like a cube! Not like a mush that will do whatever I tell it to, and if I'm lucky not lock up. I like the M slices on this cube.
My GTS2M (Custom Magnets): This cube was AWFUL initially. I replaced the springs with Valk springs, and now it is my OH main, and is near full cutting for OH. (Yes, for OH! not 2H) The magnets feel right and it is just a pleasure to use. People who have tried this cube at comp, universally loved it... It is a great cube.
My Wuque: Feels interesting. I like it, but it is a bit more locky. I suspect setup will help as I get it more under control. But I love the 3x3 stage, and I love the way the turning feels... I can feel the potential, once I figure out how to cash it in.
My Wushuang: This one... I think I have the wrong magnets in. I feel the potential for it to be awesome... but I need weaker magnets in the outermost layer. The current ones I'm using are turning the middle layers when I go to do turns, that that's not optimal to say the least. But the cube itself is really nice. I've set my PB on it, and I suspect when I get the magnets right this cube will shine. (But that means redoing the corners with weaker magnets... which I can do, it'll just take time.
Overall, I feel magnets really can help cubes, but the setup of the cube often changes, and you want to setup the cube to be faster to compensate for the magnets... for me that's rough on the Wuque, and Wushuang, where I'd already set them up to be very quick.