I cut hay for years with a New Holland 451 I bought new in 1972. Still have it and have no complaints. I still use it to cut alfalfa with. Bought a mint NH489 moco a couple years ago and started mowing grass hay with it. No complaints. My son bought a NH disc mower. I've used it a couple times. It cuts clean, and doesn't hurt plants. I've mowed alfalfa with it too. Pleased with results. It'll cut at warp speed! When it comes to mowing hay, I'm a low tech man in a high tech world....Can't get in tune with mowing @ 10mph. I do less than 25 acres total these days, and I spread that out over 4 or 5 days, so being able to mow in road gear isn't high on the priority list.
But. If I was heavier into hayin', it'd be all about the disc mower. Just too late in life to teach an old dog new tricks.