Dave,
Attached is the photo of one of mine, I use one at the service entrance where the main line comes into the property and my transfer switch is located and then the barn, garage, tractor outbuilding, and house breaker panels all have their own units. They have to be connected through a 50 amp dual pole breaker, they are designed to fail with a dead short if they are hit with a surge beyond their capabilities so you do want to check the breaker from time to time but I have not had an issue with any of mine in decades of service.
But now the bad news, the company is no longer making these mains type protectors even though they allude to them on their website so hopefully they are coming back.
ICE is now Morgan Systems and they still make a lot of great products but they don't list the suppressors I bought. I also used one of their units on the phone line when I had a landline and my ham radio antenna rotors and antenna feedlines are protected by them:
https://www.surgestop.com/
I am going to reach out to them via my business account when I get some time next week to see if they have plans of bringing the mains type units back because they work very well. Shortly after I had a new well put in back around the year 2000, the company I use started installing a bunch of VFD well pumps and the fairly sophisticated control boxes that provided the 3 phase variable speed drive to the pumps were failing at a high rate due to lightning surges. They started installing one of the ICE surge suppressors every time they switched a customer to VFD and the failure rate went to near zero. The only downside of them is the gas discharge tubes clamp very hard and very quickly so you will see some light flickering when a storm approaches as they briefly clamp the line every time a surge exceeds their triggering point.
And on edit, this company also has some excellent tech papers on proper grounding techniques for lightning protection and related subjects:
https://www.surgestop.com/tech.html
Rodger