Ah, another GPS thread... oh well
My contribution:
For your own flying, use whatever you feel more comfortable with.
For the CPL skills test you will need to do all the line-on-a-map bollockry so you need to master that. I dare say that a GPS can be a useful tool in that respect, as you can do your all your old fashioned navigation stuff as they like it for the skills test and you can see how well you did by comparing against the GPS (either during or post-flight, if the thing has a recording function).
The one thing to keep in mind is that the GPS is only as good as the batteries powering it. On the other hand, you'll be glad you're carrying a GPS if your map goes flying out the window or disappears under the carpet (speaking from experience,
my cunning backup in the form of a DIN A4 with a Google Maps printout of the whole of Northern Italy and the route pencilled over it only got me so far
)
Ah, forgot to say: I'm usually GPS-less and DI-less, including on long range multi-day navs but that's only because I enjoy flying that way.