That is a cheap dolly wheel kit. I paid 300 for my used one without tires.
I bought a 56 without a dolly wheel. But it would hang up on the tractor tires if you cranked over too hard, which I always do when I'm raking. There is a dealer over the line in Maine who goes down to PA and buys the dolly kits from the Amish. Who pull them off because they run a forecart and don't need the extra turning point. But 350 for a new one is great, I'll have to keep an eye out for another rake.
They go for 1k or so at auctions up here depending on paint and condition.
I also have a JD 660 which actually I prefer it seems to do better in thin 2nd crop. The NH is better in heavy windrows. The JD will also pick up better at faster speeds.
The other advantage to a dolly wheel is the rake isn't tied to the tractor. So if you have a rough or uneven field a dolly wheeled rake will do better than a hitch to the drawbar and way better than a 3pth rake, both of which ride up and down with the tractor. Also they are much easier to hook to your pickup for road travel.
Which the JD beats the NH again, the JD driveshaft comes off easier without a punch and has a peg to hold the driveshaft up. I always disconnect them for over the road behind a pickup.