This guitar lube is one of the best things that I've bought for my guitars. Use it every time you change strings on the nut, string guide and bridge saddles. Without it, you're scared of using your tremolo because you know that you guitar will probably be out of tune after. With it, you can use your trem as much as you want and the strings hold their tuning. The stratocaster trem is really where this products excels.
The Rene Martinez isn't cheap and you only get a small tube, but you only use a drop - and I really mean a drop on the parts of your guitar that is in contact with the strings. I think one tube will last for a few guitars over a few years and many string changes. If you work out how much that costs in effect, you wouldn't even think about it. They use it at the Fender Custom Shop, so it's definitely good enough for me.