I like Let's Encrypt, however the two are used for different purposes. Let's Encrypt helps you generate real trusted certs whereas mkcert is used for testing and local development. So for the purposes of securing a dev environment, generating a cert using Let's Encrypt is probably overkill.
M S Sripati
Experience ISMS Implementer, Auditor, Managing Pentesters, can hack and code as well. Blogger, 32K+ views on Quora
Nice article.
What are your thoughts on using Let's Encrypt?