The preview is indeed nice. I have a local editor here that also shows previews if desired, but usually work on my Write.freely instance directly.
For Release posts at Glitch -- I always write the post in text editor here, then paste on GS.
But always as a DM to my alt account. Not public, and I can see it for error checking; delete and redraft until I am ready.
Finally, remove the alt tag, and make it public, post.
Nice and without leaving any traces in public view.