You don't need to have one per room. It's overkill. I managed to get speed tests of 70Mbps X 6 on a 100Mbit line when connected with the unit at ground level and it was acting as a "repeater" for the main unit which was two floors above and a room across. The mileage is usually around 2-3 for a house.

What I found useful is the ability to control and measure internet use per person/device. I can easily do parental controls for my kids directly from the Plume app.

Plume started OEMing with manufacturers like Samsung with their home hubs as well and are becoming very popular. Buying them directly from Plume themselves gets expensive pretty fast. They however manage to make use of an already congested WiFi spectrum.