I have a 54.6mm FangShi v2 on the way, as well as a Gans Core and hardware. I already have the 57mm v1, but I wanted a v2 and I'm going to try the gans core in it. I really liked the flexible feel of it in the gans iii, but I didn't like the lockiness and crunchy feel, so I'm going to try putting this core in a fangshi. Donovan from Lubix Cubes did this too; he broke his pb by over 2 seconds instantly. The trick to tensioning is to take the whole cube apart except for the core and center pieces, push the centers down, tension it, then reassemble.
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So I got all the stuff yesterday, and I put it all together, tensioned it, lubed it, broke it in, put the core in, etc. The FangShi (or Shuang Ren as I should call it, as Baijie is coming soon) with the ganscore is AMAZING, I can see why Donovan liked it so much. It improves corner cutting drastically, never locks up, and moves even better than a fangshi without one. One problem is corner twists happen about 30% more. Overall, its incredible. You should try it. But if you do, you have to tension it like so- as soon as the nuts are on the core, don't tighten it, or it will be super tight and locky. Also, you have to put a ton of lube on the stem of the centers where they touch the core.