I used M&Ws around here for quite a few years and liked them alot.
I won't speak for the NH series, but the M&W chain and bar types were easily the best softcore balers on the market. They had a relatively (to belt balers) slow chain speed so they were gentle on the hay. The chains allowed for greater compaction of the bale material. My M&W 5x5 used to easily roll a 1300 lb alfalfa bale with the pressure turned down to mid-way or lower. At maximum pressure, I was rolling a 1500 lb bale, which rivalled the weights of most 5x6 soft core balers. The chain balers were also nice in that you didn't have to worry about broken belts. You just rolled into the field, shot some grease and oil at it, and went baling.
If you're looking at an older NH, just check over the bearings and main chains very carefully. Those chains break, and it gets costly in a hurry.
Rod