I have been using fastmail as a single personal account for the past year or so, so I don't have much to add to your technical assessment. However, I have been considering changing providers because of the political position of the Australian government. I've done a cursory search just now and can't find anything to back up my opinion, but my impression is that they have a pretty permissive stance on gov't access to data or just crappy Internet privacy laws, which I disdain. I have been thinking about making the jump to protonmail as my provider instead.