I have an electric jack on my 26 foot bumper pull toy hauler. It is pretty nice to have but it EATS the batteries. Mine also doesn't have a manual crank on it, so if the batteries are dead you are SOL. I have a generator built into my trailer though so that whenever I am going to use the jack I just make sure the generator is running or the batteries are fresh.
I have found it handy, but I also didn't really mind the crank type one. If mine didn't have the electric one on it I wouldn't have added it I don't think (easy to say since its there already
Bill