I have 3 instruments with a Zero Glide nut that I play regularly on shows and in jam sessions. My Gold Tone OB 150 has one as standard equipment from Gold Tone. Next is my Martin D custom Acoustic and next is my Washburn M3SWK F body mandolin. I did the install on those last 2 instruments. YES, you WILL have to do some fitting. Follow the instructions to the letter on this. YES, you may find it to be a pain but the gain is more than worth it. Once the Zero Glide is installed and once you start playing a few tunes, you will wonder why you have not installed a Zero Glide nut a lot sooner.
No more string binding issues, no more graphite in the slots or any grease either. You don't need that stuff anymore. No need for nut slot files either with a Zero Glide unless you get one un-slotted. You will still have to fit the Zero Glide nut so you can make it a part of your instrument. No getting around that. It is all part of the fun so enjoy the pain and take your time with the fitting. Once that is done, the action at the first fret will be perfect. Your tone will be better. You will get some sustain you haven't had before. The Zero Glide nut should be the ONLY nut to go on your instruments. I like what it does for playability and tone.
I just installed a Zero Glide Nut on my '14 Les Paul Studio. I was having trouble with the traditional *tink* and tuning issues often associated with Gibsons. Initially, I was going to try the new titanium nut made by Gibson but was told that it would not fit my '14 Les Paul. Keep in mind, I have never installed a nut before on a guitar where I needed to remove the old one. I had only fixed broken nuts in the past. I say this because I had a little anxiety when I decided to install the nut myself. The first thing I noticed was how much extra material must be sanded to get a perfect fit. For my application, I had to sand the bottom of the nut as well to get the fret to seat properly against the fret board. This may sound bad, but it is a good thing! It means that the folks at Stew-Mac realize (as I hope you do) that although these are precision instruments, there are many parts that are finished out by hand. The extra material allows for those minor variations and with a little work,
I bought the mandolin version and fitted it to my Gibson. There's a lot of extra material to remove, but the result was great. Easier tuning (the old nut had tight slots for the A strings), better intonation. Later I used one of the extra frets in the package to fix a tenor guitar. For that, I simply filed the necessary ledges in the existing nut and widened the string slots. It would be nice if Stew-Mac would also sell the offset tang frets separately, for retrofitting to an existing nut.