It seems Mouser is carrying some of them now, but those prices ... 😫
What I do like about them is they are taking the opposite approach of a lot of network surge protectors. From what I’ve been reading about lightning damage in Ethernet networks, the problem seems to be that lightning finds too easy of a path to ground, and surge protectors with ground connections want to make it even easier. When the surge protector trips, a huge current flows and anything in that path is toast.
These do the opposite and add ~ 6kV extra isolation with each isolator. A really good idea right after your cable modem. OTOH, at these prices using a fiber optic adapter ($60 for 2 + cable) to create an air gap is going to become very affordable.