Modern violin family instruments suffer from two related problems, one at each end of the strings.
At the peg end they use wooden pegs that only work well if they are meticulously fitted and maintained, used all the time to keep them from sticking, and used with the low tension strings that were the only option when the violin family came into existence. Even then wooden pegs require considerable skill to tune accurately.
With modern higher tension and steel core strings most players use at least one metal fine adjuster mounted on the tailpiece, many use 4 (or 5). This brings us to the problem at the other end. The violin family was never designed to have tuners at the tailpiece end of the strings, they drag the strings over the bridge causing damage, and most importantly they weigh down the tailpiece, and can easily triple its weight. This reduces the ability of the bridge to move freely, exactly like a mute! It's just incredible that anyone ever thought this was a good idea.
Most responses to this problem have been either to eschew the use of fine adjusters and develop skill (and snobbery) at tuning with the wooden pegs, or to try to reduce the weight of the fine adjusters.
Some modern tailpieces like the Wittner have integral fine adjusters and are made of lightweight aluminium or resin. Some very expensive wooden tailpieces use built in carbon fiber adjusters.
Both these solutions are a big improvement on 4 or 5 heavy steel adjusters mounted on a wooden tailpiece, but they still result in a heavier and less resonant tailpiece than having no fine adjusters at all.
The Knilling Perfection pegs avoid the problem entirely by fitting a geared tuner into a standard size and shape of peg.
They use a planetary gear system in the shaft of the peg, and the gearing ratio is 4:1 so for every turn of the inner shaft of the peg the head rotates 4 times.
The weight is little or no more than an ebony peg, and in any case a bit of extra weight in the scroll does little or no harm to the tone (if it did we'd remove the scroll itself, which is a lot of ornamental wood with no purpose!)
The knilling pegs come in 2 versions: a standard version with a plastic head and a deluxe version with an ebony head. Both work the same and the static body of the peg is black matt aluminium in both cases and the rotating tip and shaft of the peg is delrin (a high quality plastic), only the head material differs between the standard and deluxe knilling pegs.
You have to look quite closely to notice any difference between the knilling pegs and traditional solid wooden pegs, but there is one major difference; when you turn them they work! You can tune a string to pitch accurately with no fine adjusters in seconds, with one hand, while bowing the string with the other.