i've installed quite a few and haven't had any callbacks off it.
my parents were suffering surges from lightning strikes regularly, and i installed one there along with a few extra grounding electrodes and they haven't lost any equipment since; that was about 5 years ago.
Reading about the manufacurer's products and as much reading as you can will help over time to figure this stuff out.
this part of our industry has just been through a big change, and I think that the foreseeable future will produce even more dramatic changes as technology moves forward.
I learned this from Mike Holt:
You get what you pay for
More is better
I do mostly electrical for instrumentation and control.I don't install an electrical service without SPDs. Its paid off in a reduction of electronic equipment damage