Adjustable Taper Rulers are GREAT! They are not a gimmick.
The Taper Templates are preferred by most people BUT the adjustable is better for traveling plus it makes a great way to test different tapers without purchasing templates that you may or may not like the taper of. Then, when you decide on which your main tapers are, you can then get the Taper Templates that you will use.
We use several Adjustable Taper Rulers. The clear one is my favorite but it's more fragile than the black ones. Since the black one's clear ruler slides into the black body it is a bit less fragile.