Hey @turnbowm - I'm sorry this rabbit hole is longer than I thought. I believe my comments were based on a 2017 review which the NY Times has moved off their servers. A partial copy appears to be here:
https://www.lenkeng.com/blog/the-best-surge-protector-reviews-by-wirecutter/
Also, note in the current link they reference the 2017 article and have a picture of the guts of a ZeroSurge unit. I repeat that Furman does use Series Mode Protection. They also have a sacrificial MOV for an edge case. An EE explained it to me as rare but possible situation the old-school series mode protectors would not cover.
If you have a Brickwall or ZeroSurge unit, it is probably still in great shape and will continue to outperform most surge protectors out there, you absolutely should leave it where it is! If you are buying new though the Furmans not only have Series Mode Protection, and Extreme Voltage Shutdown but also additional HT/Audiophile friendly features.
I'm sorry this is about all I can do at this particular moment. I'll try to find the links in the Wayback machine later.

