Not rocket science really. Every bit of grunge on a propeller is reducing the efficiency of the blades and making it harder for the engine to rotate them at optimum efficiency. All very well to polish your propellers up but in time the continuous polishing is going to have an effect on the strength of your propeller blades. Proper cleaning makes all the difference and the right advice about keeping it clean can save you a lot of money. It might be Propspeed if you want the best but we can give advice on other ways of looking after your propellers..
Many propellers require very little force to bend or nick the blades. A small piece of driftwood can cause a damage way beyond what might be expected. But you cannot just bash them out.
Your boat might have been propped for the last bit of speed but you are more interested in slower speeds with fuel savings. The design of propellers is improving all the time and there are large gains to be had from keeping in touch with a propeller specialist..