You have to understand rental companies really don't know **** about concrete grinding. When edco did their march across the country years ago selling these "new fangled" grinders, rental companies ate them up. Edco finally came up with some tooling that actually "kinda" worked. Most rental companies didn't want to bother with the diamond tooling. Because of how the duel heads on the larger edcos don't float, the large foot print on these causes one to grind deeper to hit the valleys of the uneven finish of the concrete. A single head edco will outwork production wise than it's larger brother. Edco has since come out with a floating head attachment but the rental companies see this as useless.
If they have a single head edco, I'd go for that. It's smaller foot print will speed the grinding. No matter which one you end up with, down pressure is your friend. (Add a couple bags of heavy on top of the machine.
