I read their entire website and still have no idea what precisely Plume is or what they're selling.

"What makes Plume different from my traditional Wi-Fi router or extender?

Single router Wi-Fi systems can give you the speed you need as long as you’re close enough to the router. Wi-Fi extenders or repeaters can improve coverage, but are often complicated, unreliable, and degrade performance. Plume is a cloud coordinated Wi-Fi system that replaces your current router and gives you stable and consistent Wi-Fi coverage and speed in every room within your home using blazing fast tri-band SuperPods coupled with auto-channel hop technology."

If I understand this word salad correctly, it's a router which uses a cloud service to auto-configure itself.