I think it looks cool, too, but I think the adapter design is crap. On all large machines that routinely use duals, the outside tire is attached directly to the axle, instead of the wheel next to it. This puts vertical loads and shear forces on each wheel, transferred to the axle, rather than the outside wheel transferring its forces to the inside wheel, and then to the relatively short lug nuts. A better and stronger way of doing it would be to make a hub extension. Mount the inside wheels, then use longer lugs to bolt the extension and inner wheel to the main hub, then mount the outside wheel to the extended hub. Loads on the outside wheel go straight to the axle instead of through the inside wheel first. It would be more expensive, but put less stress on the assembly. And what about driveline load; obviously the doubled footprint will add tractive force, although it will also increase flotation, another reason to load the tires if you go this route. With that much traction available, can the transmission handle it, or will you be up against the PRV in high-load situations, like loader digging work, or pulling a heavy implement?
The kit he used also screws up the ability to mount wheel weights, since those bolts use the same holes you bolt the center weights to.
Duals sure will help on hillsides, I bet. You would probably start sliding sideways long before you rolled over. In another video this guy made, where he talks about mounting duals, he shows the 1025R with dual fronts as well as rears, just has the tire/wheels resting beside the mounted ones. Maybe Deere should make an articulated 1-Series, a "mini 9620"