I’m not using anything that you would recognize as a full-featured client. I upload twts with hut publish, “publicise my user agent” with manual curl invocations (when I remember to) (thanks to @movq@www.uninformativ.de for the informative guide https://www.uninformativ.de/twtxt-mention.html), and as for following other people’s feeds, I still haven’t decided how I’m going to do that.