I have a 12V retractable Max Power (I think it is a French brand) on my Beneteau
461, a 20k lbs boat. Have been using it since 2005 and it has been wonderful.
The primary reason I chose the retractable style was the shallowness of the hull
forward: A tunnel type bowthruster would have had to be installed too far back and I didn't want the hole impacting sailing performance. As it is, this one is located right at the bow and extracts to about 3' depth
and doesn't cavitate.
As far as the 12V part goes: I didn't care for adding a whole new system of hydrolics, etc to the boat. As the boat comes with a 12V system already, it - in my opinion - was a good match.
Because of the cable lengths involved, a 12V system running a hefty electric motor
suffers from a healthy voltage drop - even with gauge 1 wire. A battery
located closer to the bow thruster became necessary and I installed an Optima (blue top) and haven't had any issues to date. If you have 24V, it may offer different options.
Another point I like is the quietness of the electric
thruster: Unless you are standing next to the boat, there is no way to know that I am using a bow thruster; makes me look better than I really am
The downside was the significant cost of the thruster and installation