Just to throw the cat amongst the pigeons then, if using a GPS is 100% legal along with other navigation data(maps or whatever), then would using one would be deemed as "cheating" for the CPL skills check, similar to using a calculator in a maths exam!! I think the answer is use whatever is available at your disosal for the skills check, and if the aircraft being used has a GPS fitted...use it, but check with your examiner first.
Don't get me wrong,I'm not against GPS's, I use both maps and a GPS,when available, if it helps with navigation then that's a good thing. However remember to look outside at the weather etc, failing to divert if the weather conditions are below minima is a fail.