I have Factory Connection stuff, and I love it. At the end of a moto, I am less tired. I can also ride harder, because of vastly reduced arm pump. The biggest thing, in my opinion, is how much plusher the forks are initially, but yet how much they resist bottoming. The biggest downside, I think, is the price. I expected it to be around $400, but after they hade made various updates, and replaced probably 20 different seals and bushings, the price came to $525, and that is without changing springs.
I live locally, so I did not ship it, I drove the 7 miles from my house to the shop. I was very surprised by the size of the place. It is a fairly tiny shop, with probably 3 or 4 rooms... It did not look any larger than 2 or 3 garages, but I really could not see the whole place. I dropped my stuff off at probably 11 or 12 in the morning, and by 4 it was ready.
Honestly, the difference is unbelieveable. These guys work magic with suspension, but they charge you for it. In my opinion it is totally worth it. I have ridden other YZ125's with other company's revalves, and the factory connection stuff is definatly superior. The shock stays planted, no matter what the terrain, and is very smooth. The forks are the same way. It does not bottom very often, and when it does, its not hard.
I have ridden with a sales guy, a machinist, and the owner, and they are all pretty good riders.
I think it is worth it, but it is still very expensive. If you have played with the settings on the stock suspension extensivly, and have not found anything rideable, then send your stuff here. Something I never did was play with the stock suspension, which I should have done first, but it is too late now.