I tried Meshtastic here in London (UK), but was struggling with anything more than 1 hop away. There's no coordination, everyone's using the long fast preset, etc. Then found out about Meshcore, flashed the firmware, selected the UK narrow preset, and it's a day and night difference.
Still wouldn't rely on this for anything serious because it's not reliable at all, but it's nice to be able to send a message across the city or to the other side of the country.
Similarly, I put a repeater in an upper story of an apartment building in Boston and am reliably able to talk to people over 10+ hops. Right this second I'm able to talk to someone 99.5 miles away in Vermont.
We had to create different channels for different regions (connecticut, new hampshire, massachusetts, rhode island) just to keep from having hundreds of messages in a single public channel when posts are generally about local things.
Unfortunately it doesn't fix congestion issues completely, repeaters still repeat everything (and can't listen while transmitting) so packets from connecticut still put traffic onto the entire mesh all the way to new hampshire, but at least it's better organized.
It seems like there are some ideas to help with congestion, maybe making channels region specific (repeaters can be programmed to only repeat traffic with a certain region code) but for now it's shocking to me how far I can reach with a 0.125W radio.
But yeah, it's not "reliable", that's what TCP/IP is for =) Definitely a toy network for now, and a single malicious bot on the frequency band would absolutely wreck it. Or a single high power jammer sending out noise at just the wrong frequency. Definitely a fun project for people who would do ham radio if they had any interest in taking a test...
I wouldn't use it for emergencies though, it's theoretically a backup if the cell network and internet go down but the reliability just isn't there and I suspect never will be.
Still wouldn't rely on this for anything serious because it's not reliable at all, but it's nice to be able to send a message across the city or to the other side of the country.