I suggest that you read Nigel Calder's Boat Owner's Mechanical and Electrical Manual for a thorough explanation of what they are, and how they work. They will protect you from other boats when you are on shore power, but they will not protect you from dissimilar metals on you boat.
I have a Prosafe 30Amp unit on my boat, and it seems to work well.
I have also un-bonded all of my through hulls. I don't recommend that anyone else do this.
I have the Charlie Wing book and use it for reference.
RE: bonding of through hulls. I recently hauled out to re do the bottom. No zincs left at all and discovered pink on the gudgeon and strut. Also that the gudgeon had slight movement. In removing and resetting the gudgeon I found that the bonding cable between the gudgeon and strut (and then to the engine) had corroded and separated.
I'm really trying to figure this out, but find conflicting information.
I have an atomic four connected to a stainless steel drive shaft held by a bronze strut driving a bronze propeller (which also showed some pink). All of this bonded with #6 wire (which was showing signs of corrosion). The pearson bonding diagram (which does not exactly match what is in place) shows chain plates, through hulls, grudgeon and strut bonded to the engine and then to a keel bolt.
The only AC on my boat is the battery charger and any hand tools I might be using. I never leave the shore cable connected more than overnight and go weeks without using it at all. The DC grounding bus is connected to the engine. Any DC leakage should go down the shaft which has two new zincs now. So my concern is what is causing the galvanic action on the grudgeon, strut and propeller and how do I stop it.
One last detail. Two plus years ago I used Petit's zinc anti fouling paint on the strut, shaft and strut. I was pleased with its performance and have used it again. Could this be a contributor to my problem.
And another detail. I sit between two neglected boats that are continuously connected to shore power, but have no knowledge what is going on inside.
I appreciate any help you can give,