You will either LOVE or HATE a cart. Builders like them because they are maint free for the first season...THEN you have to clean them So builders push them, not because they are better for you but because they are better for THEM. You have no problems before the warranty runs out. Plus they don't have to run all the plumbing you need for sand or DE to backwash them. That doesn't make carts bad. There ARE tricks to make them easier to use.

I had a little tiny cart on an Intex and hated it. I now have sand and wouldn't have any other--well, maybe DE. But my dad had DE for decades and wouldn't have sand or a cart.

Your builder doesn't have to live with your choice--you do. Make the choice that YOU can live with.