Well, here is a "yang" review. I absolutely HATE this stuff. I tried to (did) use it for years. What I started noticing is that once you use it, it doesn't matter if you have the strings on for a year, they feel greasy, they are slick, and while they feel "slick" they have a different sound (sort of a squeak) to them when sliding up and down a string.
I DO NOT like the feel of the strings once it has been applied, but worse, notice strings slipping out from under my fingers on bends. I could go on, but don't need too. Like I said, I DID use it for a couple years, convinced by others that it was a positive thing and that I needed too. Boy, when the stick is brand new, BE CAREFUL! If you "coat them good" the first time, IMO they are completely ruined. ONLY a very light coat of this stuff is even tolerable to me, and even that is worse than not using it.
What I've started using instead and it is a complete game changer for making your strings last many times longer without making them feel like you coated them with grease, is a Connoisseurs Silver Polishing Cloth. This thing is the best thing ever for strings. Use it when you put them on (you won't believe how much oxidation and crap comes off brand new strings!) and then a quick use after every few playings. I've had strings last WAY longer than you'd believe and still be shiny silver and still sound great.
To each his own. Like what you like. No right or wrong, blah blah blah. But I can't stand Fast Fret and this is an absolute GODSEND for guitar strings! Just do exactly what it says, each side has specific purpose.