We had a 7' model when I was growing up. Cut a ton of acres (25/year x 20(?) years) without any problems. We did have a couple sets of knives so that we could always have set of sharpened ones on hand, and so we could swap them out every spring. Other than routine maintenance, I don't ever recall having any problems at all - no bad bearings, broken belts...'Though, we always stored ours inside.
I recall my dad saying that he thought a conventional cutter with rollers probably made hay faster (used to take us 3 days minimum - one to cut, one to flip it over, and bale the third), but he thought the cutditioner was more user and maintenance friendly.