i´ve used a holesaw for the side blowholes of my own case. its good for cutting, but it´s difficult to get such a tight fit of the hole as the dremel does,it goes off it´s path upto 3 mm and getting one of the right size is rather difficult. i prefer the dremel. the professional has electronicalcontrolled rpms which can be set by a plus and minus button from 5000 up to 33000 and read out at a display at the back of the tool (see pic).
it also provides a softstart for more power when starting cuting or drilling. i did fanholes for a friend with that baby and it was quick and quite fun.