Hey @mitch2
Wouldn’t this work just as well inside of the house if inserted in-line before the modem? Ground it to the copper water pipes?
Would you rather have a surge enter your home first, and then find a path to ground, or would you rather have it find a path to ground outside? By law there should be an external grounding block which is the ideal place to put one of these. Obviously if you are an apartment dweller you can't do that, so you do the best you can.
There are many Ethernet isolators available - some using transformers (like in NA’s Muon Pro) and others using fiber optic isolation like in the GigaFOIL range of Ethernet filters (i.e., fiber optic isolation link = FOIL). The price of these filters varies significantly.
Convenience and cost matter. The issue with isolators marketed to audio consumers is that they are not tested the same way that isolators for patient care devices are. The latter are tested to ensure 4kV of isolation from input to output, so if using an in-line Ethernet isolator make sure it’s tested to IEC 60601 (I think there’s a UL equivalent). Everstar is among the most affordable.
Between my modem and router I use Ethernet to Fiber isolators with a 1m air gap. At the end of runs from there to my home office or HT I use the Everstar isolators. About the same price per use. The fiber adapters run $20 each, plus the fiber optic cable.
Based on the latest research, avoid any Ethernet isolator/surge protector that grounds the signal, as those can be more dangerous. Since I don’t know which is which I never use the built-in isolators in power strips.