I have two tractors with self leveling loader, or so they are advertised. One is mechanical and one is hydraulic. The hydraulic one can be turned off, which I find to be a good feature on some tasks, the mechanical one is full time. The hydraulic one is much more accurate.
My opinion is that if you plan to use forks often then it is a great option. I also feel that with an experienced operator it is not a necessity but convenient. If I were buying my last tractor, I would invest in it. If it were a mechanical system I would be less likely to invest.
MarkV