The MF 50 is a bit less power than a 961, while the 65 is probably a bit more. Neither are particularly collectable.
Diesel versions of either are more valuable as workers as both have highly regarded Perkins diesel engines. Gasoline versions use Continental engines and parts are becoming more difficult to find and expensive.
Both tractors use sliding gear rather than constant mesh transmissions like the Ford and are known to stick in two gears at the same time if shifted out of reverse quickly. Usually they can be freeded up by rocking back and forth while prying on gears with a large screwdriver through the oil filler hole. You will find the MF sliding gear transmissions rugged but not as user friendly as the constant mesh transmissions used in the Ford.
I believe that live and non live PTO versions of each were produced.
PS systems are problematic and expensive to repair.
As workers, the 65 will probably do as much work than a 961 while a 50 a bit less.
Make me an offer on my 961 if still interested. The worst I can do is say no.