Some valves do limit the ability for multi functions! Some don't, it is wise to double check as manufacturers might change the valve style in line with little notice.
The mechanical is a positive self leveling where the hydraulic is not although very accurate they both seem to work quite well. That is as good as they can as the best operator still needs to keep adjusting level for digging, the level bottom changes with the tractor position, the best said it might keep dirt from spilling onto the tractor hood when raised up. At the time that you have the load raised aren't you normally dumping the load? After you do this for a bit you learn, so is it worth the cost to have it? For many it is not, the mechanical although simple as it is with extra arms built into the linkage often restricts vision over the loader to the sides of the front of the tractor where the hydraulic doesn't hinder the vision.