Mesh typically sends/receives only what is necessary to each node and to each connected unit, which reduces noise and interference.

Extenders send everything everywhere all at once, lots of noise, they have no smartness with regards to who is connected where.

I’m not sure what a router bridge is.

In my own anecdotal experience, extenders were garbage for overall throughput, but yeah, they cost quite a bit less. My current mesh gets anywhere from 450-950mbps across 3ish acres of coverage which is more than sufficient.

Hopping. In a mesh, your device is “transferred” to the nearer/stronger signal even if there is still a weak signal from the original AP. In an extender, as long as the AP is detectable, your device will cling to it, which may result in suboptimal signal and speeds.

I’ve never even heard the term ‘router bridge’ before. A wifi extender is terrible because (generally) it halves the amount of bandwidth available aka the speed.

The only thing ‘mesh’ systems do that outside of a properly designed network will not happen is that a device will seamlessly hop from AP to AP. This is critical in most business/enterprise environments, but in a home you can just name the different APs different names and manually choose the right one because otherwise you’re generally paying 2x to 4x as much for the convenience of it automatically hopping around as well as for the limitations that most mesh systems have in relation to normal router/ap features due to their target market to be basically consumers that want to throw money at a problem vs correct the problem (aka give me a pill to fix it because I won’t exercise).