Comment by creeble

I don't have a video link handy, but this British mod dude has a very brief summary:

Guide.Zenn22.Shop (redirects to a steam site I think). He has many modded F91W's on eBay.

I have one "fake" F91W, it's actally SKMEI branded and keeps fine time. Not sure I believe his claim that the fakes are so inaccurate, but maybe.