I agree with almost all KellysEye says. I think the message is that for most boats an expensive grounding plate will add little or nothing except perhaps simplicity of installation.

But I have a dynaplate on mine! Because it is a wooden boat with almost no metal permanently immersed; in fact 2 seacocks is it. I could run copper up and down the bilges and I know that would be at least as good as the dynaplate, but it is practically very difficult to arrange.