For over a year now, I have been using Purple Extreme and it's the third dry lub I have used. The others, both recommended in various places were ok to apply but seemed to need quite frequent applications, ie, didn't seem to last on, or in, the chain very long.
On using PE for the first time, I immediately noticed that gear changing was much smoother and quieter so that impressed me. Whether or not it would last any time, I didn't know but I can now say after a year's usage, the somewhat expensive little bottle is going to last me a long time.
My derailleur gears have needed very little fettling since I started using PE so I really can't knock the product although it comes with quite a lengthy American sales blurb. Like the well-known outdoor stains and varnishes ad claims, this stuff also 'does what it says on the tin'.....or plastic bottle in this case.
Tom