What is mesh?
A basic feature of mesh is that every node in a mesh-network can simultaneously send and receive data. Each node is connected to each other node. In such a network, where everything is connected to everything, the best (read: fastest and most reliable) route for sending and receiving information can always be found thanks to clever software control.
In theory, therefore, a mesh-network is much more reliable than an ordinary wifi network. In case of a node failure, a mesh-network is able to quickly determine another route on which your data can be transported. This requires a great deal of processing power, and there is a price to be paid for this. For this reason, until recently we found mesh-systems mainly in the business market, but now the required computing power is affordable enough for the consumer market.
Is every mesh-system the same? That is certainly not the case. The differences are not limited to AC classes and theoretical WiFi speeds either. An important distinction between mesh-routers is the presence of a so-called wireless dedicated backhaul. In fact, within a mesh-system there are two communication flows, one for the clients that communicate back and forth with the mesh-nodes, and one for the nodes (compare this with a network with access points, which are connected to each other with a cable). With cheaper mesh systems, both communication flows cross the same connection and therefore have to share the available bandwidth. This means that when this connection fills up, there will inevitably be a delay. This does not benefit the connection between the device you are using and the Internet.
For this reason, more expensive mesh systems use the aforementioned wireless dedicated backhaul, a separate connection for communication between nodes. Some mesh-systems offer the possibility to create such a dedicated backhaul via an Ethernet cable. This is of course an excellent option in terms of speed and reliability, but it does mean that you have to start pulling wires. As we saw earlier, this was precisely the reason for opting for a mesh-network. A wireless dedicated backhaul is precisely what makes mesh attractive, with the help of a fixed, separate radio connection.