I cannot help either other than with general advice. Usually when a pool builder is leaning away from something and toward something else, there are two possible reasons:
1) He doesn't know how to install one product properly, but knows how to install the other.
2) It's to his benefit to get you to install his product. That's not necessarily bad. A Chevy dealer knows Chevies. A Ford dealer knows Fords. But a lot of builders push cartridge filters because, for the first season, you never have to tend to it....and then when it becomes difficult and expensive the 2nd season, the builder's warranty is over.