I've used a Jepp type CR5 - the smallest of the circular whiz wheels - since 1987. Oz instrument rating exams and Oz, USA & UK ATPL exams all passed without a hitch.
Much more convenient than the slide types. And pocket size! My experience is that they're more accurate than the CRP1 (or is 5?) that is favoured in the UK. Also some ATPL problems require fewer steps than the CRP requires.
Oh yes....and you can quickly & easily use an off-track DME to provide on-track groundspeed using a CR type.
