As the licenced plumber the materials that you use should be up to you and not the builder, if something goes wrong they will point the finger at you because you installed the product.
If CPVC is both legal and suitable for the application and you are comfortable using it then go ahead.
Sylvan, as always, has a very good point in that copper is a tried and tested material and the cost benifits of using other materials on a smaller project would not be great.
For every argument that supports plastic materials, there are an equal amount that support copper.
But at the end of the day, you have to be satisified that you have installed the best product for the job, so if you are uncertian about CPVC, then do not use it.