Great stuff. Been using it for years.
Stabilises the tuning on my guitars with non-straight string pull. My Gibsons hold tuning for days, when this stuff is in the nut and saddle slots
However, note that this stuff isn't a solution for poorly cut nuts. If you hear a ping at the nut, when tuning your guitar, take your guitar to a tech first, then use this second.
Some people think it impacts on tone. I've never noticed any impact, personally.
Highly recommended!