https://secure-contracts.com/program-analysis/echidna/index.html and https://secure-contracts.com/program-analysis/medusa/docs/src/index.html will give insights into how to use the tools.

You can find real world usage of the fuzzers here: https://github.com/crytic/echidna?tab=readme-ov-file#public-use-of-echidna

Echidna has 2.7k stars on github, and 40+ contributors