I've recommended them in the past and any boat in my future will have them.
If you really measure the output of your electric bilge pumps, they will only hold back sinking on minor inflow. They work in either direction, so will work either forward or reverse, since it acts like a centrifugal pump with some amazing specifications.
Yes, you do have to build up the area where the pump shell mounts, and provide a good path to exhaust the water being pumped out of the boat. You don't have to pull a shaft since everything is clam-shelled and splits to fit around the shaft. It may be inconvenient to mount on a V-drive boat since it would be under the engine.
Yes, you do have to leave the prop shaft spinning for it to work, but chances are, you're implementing plan A while it pumps hundreds of gallons of water overboard as you head to the beach.