Synapse (the original python matrix server implementation) gets a bad reputation because it used to be particularly bad - we've done loads of work to improve it though, and these days it's pretty reasonable. https://matrix.org/blog/2020/11/03/how-we-fixed-synapses-sca... and https://twitter.com/matrixdotorg/status/1434912387933560837 gives some info.

On the other hand, both Dendrite (Go) and Conduit (Rust) are usable on the public network, despite being beta. There are some missing features, but people can and do run them for real, and both projects are super promising - and with more contributors, they'll land even sooner.

Needless to say, this has absolutely zero to do with ITA's Matrix flight search system :P