This is a special, custom-made guitar tuner that can be installed onto any pre-existing guitar headstock (assuming that your headstock is where the tuners are located, this is not always the case). The cool thing about these tuners, at least initially, is that they clip the excess part of the string that isn't used after you re-string. Locating the constantly-missing pair of wire-cutters always somehow seems to be a hassle for me. These tuners solve that problem easily, and make cleanup far easier.
Beyond the clipping feature, the hands-down best feature of these tuners is the fact that THEY KEEP THE GUITAR IN TUNE. I've been happy with many of my tuning knobs and tuning systems, and they all have their merits, but I really can't believe how much better this system tends to be. I've been able to play my Tele for 3 days straight and not having to tune once. That's a remarkable accomplishment in craftsmanship on the part of Planet Waves. Considering how many times my guitar has gone out of tune on me at extremely inopportune times, these tuners are a godsend.
This is assuming, of course, that you are willing to go through the relatively painstaking process of installing these. I personally had some professionals that I trusted do this work for me. I deliberately selected a newer guitar that I wasn't necessarily in love with. This is mainly because I didn't want to drastically alter the look of my old Strat, or my relatively old Les Paul. Thus, I used an early 00s tele that I wouldn't have minded abusing slightly. There is a noticeable change on the headstock, one that would be enough to severely alter the look of a vintage instrument. While this guitar is sort of still being broken in, my older ones are already sort of set in their ways, and would not have handled a drastic change such as that without playing or looking worse. So if you don't mind some heavy remodeling in the name of great intonation, you should definitely get these tuners.