A typical consumer "repeater" has only one set of radios and can't multi-task. It receives a packet, flips to transmit mode, then broadcasts that packet. By design, this will cut speed in half -- each time that a packet traverses a repeater. Mesh access points can simultaneously send and receive. The mesh attempts to find a minimum time path through the mesh. Traversing a mesh node implies a slight latency, not a wait for the whole packet to arrive before sending delay. If a node goes down, the mesh will work out a new topology.

The appeal is that one does not need to run wires and a wireless mesh will minimize the performance hit compared to the "repeater" approach. Of course, wired is always faster and more robust -- when practical. Mesh is a great solution for renters.

In the real world things are not quite as rosy as implied above: Here are some thoughts

My experience with mesh has been much better than with simple repeaters -- but I will always wire when practical. While I will encounter previously deployed repeater systems, I have only installed one "repeater" (at the customer's insistence because it was already onsite), but I regret that decision because it has caused trouble.

Some of the products will attempt to use dual band to work out a "backbone" scheme. This approach will avoid many of the collisions. and could improve roaming.

Some further food for thought, but note that this review is using the older, not the current Eero product.

Slightly related to the above:

802.11r
Apple devices and roaming