And only Silva compasses do this? As to measuring distance on the ground and the rest you need a MAP not just a compass. I can walk in a straight line except when sloshed.
Well if you want to take bearings or walk on bearings, then you need some type of protractor for reasonable accuracy. And the definition of reasonable depends on the use. For seeing whether you should turn left or right on a path, then it's probably overkill.
If you want to locate yourself on the map without GPS, and you can see landmarks, but are not near them yourself, then a baseplate compass is probably a good idea. You could use a prismatic compass, but often they are slower to use.
I admit that I did get a Recta compass instead of a Silva one as my main compass, but it's equivalent - I find the mirror useful as a mirror and it folds out longer than a normal baseplate compass, but most of the time I use it as a baseplate compass.
As for the "walking in a straight line unless sloshed" bit. Are you sure? What about in fog over rough ground?