It is a new Tengy1, with better corner cutting, click magnets and auto-aim
The Gan12 Maglev is light, fast, has weird feeling magnets and an aimbot. It is also an awesome cube. Despite its lightness, the pieces feel more solid than on its predecessor, and it is less crunchy as well (squeezing it doesn't produce that distinctive crunch crunch of the Gan11). The speed is very fast so if you're used to "normal" cubes you need to lower the strength of your turning significantly. And some lube to slow it down a bit cannot hurt either. I found myself +2ing a lot of solves because my AUFs were a bit too enthusiastic and easily overshot by one or two quarter turns.
The magnets are... weird. Changing the corner setting (only magnet setting that can be adjusted) doesn't change the auto-homing mechanism, and it hardly changes the clickiness feel. It does, however, change how well the cube keeps its shape when abusing it a bit. Given the very light pieces that was an issue for me as I would generate lockups due to the lower layers borking out as I did my algs badly. The "springs" feel very very similar to the first Tengyun (with the good spring swapped): a bit stiff but with no friction. Here the customisation options are much more effective: the cube changes feel g a lot depending on what settings you use (with the travel distance playing more of a role than spring stiffness).
The comparison to the Tengy is relevant given that they are the 2 fastest cubes I've ever been able to use, but in contrast to it, the Gan12 has fantastic cornercutting, and besides the cases in which I mess up my cubeshape during algs, it rarely locks up, which tends to happen to me a lot more on the Tengy. The overall feeling of the cube is very different from other Gan cubes. If the Gan11 was a steroid version of the X/XS that removed most of their flaws while keeping that Gan feeling (at least it felt so to me), this one is a very different cube.
Then there's the UV coating. I had forgotten how it feels to be able to use a cube out of the box without it being a slippery piece of crap until the frosting wears off. This feels great (although the difference compared to a worn out well broken in cube is not huge), it is an added "quality of life" bonus that is just nice to have from the get go.
Which brings me to its price. This cube costs a lot. You can buy 2-3 stellar cubes for the same price. So if money is a concern, just get another cube. If you want something as fast, get a Tengy1. If you want the same forgiveness with inaccurate turning, get a WRM. But if you can afford it and want a cube that is great, this is something you can dunk a month worth of coffee into and be happy with.