I had a Dotan system on my M 6.0. If you sail in an area where you can put them down and not worry about ever having to sail with them in the kicked up position I'd rate them a 4 on a scale to 10.

Some of the problems. When kicked and trying to steer they flex a lot. The rudder blades float so when they kick they raise so high as to make it impossible to steer. You don't want to be around me when that happens. ( I understand why they float) If you snug up the pivot screw you can stop this from happening but then they become difficult to operate. The screws that are part of the pivot mechanism bent. I also broke a rake adjusting screw when hitting the bottom. A lot of small parts.

my 0.02