The translations are pretty good. The desktop browser extension used to annoy me, but the problems I used to have are fixed.
My original comments...
1) I cannot translate a website or tab within the browser. UPDATE (10/2020): for the past couple of weeks I have tried using the new feature "Translate this page" which is supposed to solve my problem. It never works for me, but I hope it will get fixed soon. This is just what I wanted! UPDATE (8/2021): full page translation works on the desktop! Hurrah!
2) The Safari extension crashes randomly. Every time this happens I have to close all of my tabs and quit Safari to get the extension to reappear. UPDATE (10/2020): I have been in contact with the developer via their support email. I have sent several crash logs, but so far I have received no response about the cause of the problem. They stopped corresponding with me after a few emails. I hope they will not ignore my problem. UPDATE (8/2021): it doesn't crash anymore! Hurrah!