They are unnecessarily complex most of the time. I haven't used mine since getting my PPL.
Instead I use a device called a wind protractor, which does everything I want, and which can easily be used in the cockpit. It won't do the various "extra" things that the whizz wheel can do (TAS, density altitude, mutliplication and division, etc....), but in every day flying in Europe in a light single that really doesn't matter very much.
The wind protractor was shown to me by the CFI of the club where I did my PPL, who taught me the whizz wheel thoroughly, then told me to use the protractor instead. Sound advice!