Just as two lawyers interpret a law differently so do pool professionals.

The larger filter will easily go a full swim season before it needs cleaning and is rated for a much higher flow rate than one with a third of the swept area.
I'm not saying that the 150 isn't adequate because it is. I use larger filters so the buyer can clean in April and October. IMO, the 150 owner will be cleaning much more often than the 520's owner. I'd rather clean more elements less times than one element more times.
What I've found is that most buyers completely forget about their filters. When they call me back every time the filter gets dirty it's assumed that I'll clean it for free until the end of the first year. I find it easier to pay more for the bigger filter knowing it'll go years without cleaning if necessary.
I've seen lackadaisical homeowners who'll go 3 or more years without cleaning their filter. These large multi-cart filters will circulate even with more dirt in them than you can put in a full size wheelbarrow. I've seen it firsthand on many occasions.

I'm not trying to imply that all homeowners are the same, I'm going by what I've seen year in and year out. I've had plenty of homeowners who'd just assume not clean and simply pay to have the elements cleaned or replaced. For those the larger filter makes perfect sense. You don't have to pay for filter cleans as often. In our area a filter cleaning costs the same whether it's one element or 4 elements. If I were in the service and repair business in addition to pool construction I'd install smaller filters and cross my fingers that I get the call every time the element gets dirty and needs cleaning.

See ya,
Kelly