Im probably not the best person to ask especially since my opinion on gan as a whole is not very good, ill give you the facts and then some opinions afterwards.
FACTS: The Gan 356M is the same mechanism as the gan x with the medium magnets installed and a matte finish. The magnets aren't interchangeable but it comes with 4 numerical IPG nuts if you buy the full version. Yellow, Green, Blue (pre-installed on both versions), and purple. The lite version is the same cube but without the extra nuts
although you can buy them separately later from TC if you are unhappy with blue.
OPINIONS: Gan cubes are very hard to use and for the most part the only reason people main them is for clout. Their cubes have decent performance but get strange lockups and can be very unstable at times, not to mention they don't respond well to lubricant at all. I would advise against getting a Gan because of those reasons and the WRm or Valk like fits more cubers better and have better performance at a lower price. Gan as a company has been rather frustrating for me ever since the 354. For some reason, they add features that are either ripped from other companies or set back the ability to cube on them. For example, I think their megamix performs just as good as the galaxy or yuhu v2 but the grip is awful due to the lack of ridges and incredibly slippery matte finish. Gan has also been recycling designs of their corners since the 356 S and edges since the Air. The only differences I can find is stickerless variants, different plastics being used, and placement of the honeycomb pattern/ridges. Many people will disagree with me on this point but Gan is the apple of cubing without the things that make Apple products good, their ease of use. However, they do the same thing that Apple does, "Innovate". The only thing that GAN has done innovative in the last 4 years is to simplify spring swaps and make the first interchangeable magnets. However once the EDM blew the GAN customization system out of the water, gan responded by outright copying the magnet adjustment feature and calling it a day.