I have my beloved fretless one piece maple 1978 neck Precision bass that is cursed with a buzz on the A string. It appears between the tuning peg and the nut.
I got the neck years ago without tuning pegs and had purchased a set of Schaller Original F-Series BMF 4L NI.
When came the time to extract one of the thrust bearings (the pieces that look like a kind of tube) and insert it into the string retainer, I realized the diameters did not match for just a few 10th of millimeters! I then needed to grind the diameter of the string retainer just a little over 17 mm so that the thrust bearing can be inserted. It took a dremel power tool, a pair of pliers, protection glasses and 20 minutes to get the job done. The rest was a breeze to install.
So in the end, if you're not equipped with adapted tools or not very handy, you may have a bad surprise if your bass is equipped with Schaller tuning pegs. It should work fine (I guess) with Fender tuning pegs.
Apart from this annoyance, this things gets the job done by breaking a little more the angle of the string and without changing too much the appearance of the instrument which is what was advertised in the first place.