Yuck. I’ll bet all those dirty dirt stones made a mess all over your house. How well do they compare against a more modern and advanced piece of technology like Sharp Pebble?
I’m totally not jealous btw.
I've not used Sharp Pebble specifically, but assuming they're a similar affair to other synthetic waterstones, here are handful of random thoughts...
Almost all natural stones are based on silica as the abrasive, which isn't as hard as the Aluminium Oxide or Silicon Carbide in synthetic stones. This means that natural stones tend to be a little slower.
There are certain circumstances where that doesn't necessarily hold true; Coticules, Turkish, and Washtias can all be a fair bit quicker than comparable level synthetic stones.
Natural stones are pretty much always going to be harder than synthetic stones, not many of them self slurry. And that might make them a little more difficult to use, or at least take a little practice to understand. Though they wear considerably slower than the majority of synthetic stones.
Most historic natural stones are relatively fine. Again there are a few exceptions, but coarse natural stones tend not to be all that good in comparison to coarse synths (imo). The majority of the stones in this thread would be finishing stones for either knives or razors.
Natural stones often have a wider range than synthetic stones. Depending on how you use it, a natural stone might do the work of 2, 3 or 4 synthetic stones.
I do use synths, though not a massive amount any more, except when doing heavy repair work, and the reason for that is: the Washita. Washitas are flat out extraordinary, and can work from the mid to high 100s up to the mid 1000s in a single stone, no need for a progression. For sharpening knives I probably use Washitas as much as all the other types of stones put together.
There are obviously a about a billion other things, and different types are different from each other, not everything here would be suitable for knives.