Your friend may want to review the
Pool School - Pool Filter Comparison page. In short, while the sand is convenient for easy backwashes, there are other seasonal considerations that come into play (i.e. deep cleaning the sand, potential spider gasket failure, laterals, etc). Then there's the additional use of water, perhaps not a problem in your area but for some very important. Cartridge filters, especially multi-cartridge, have come a long way. Some basic disassembly to gain access an rinse off the cartridges is about all. But in the end, a lot of it is personal preference. Hopefully that page will help your friend out.