I have never had any issues with CP2021-based TTL boards and I have used quite a few, even very cheap ones.  The main potential issue is that they don’t (easily) implement auto-reset.  Sometimes they also mark Tx and Rx the opposite way to the way you expect (they mark what you should connect to rather than what they are on the CP2021) but that is consistent in a batch and easy to diagnose.

Leonardo compatible boards would save the issue but I have never seen them approaching $5.  If you have a cheap source of those I would be interested to know.

Ugi