It is a one person operation but it is very stable, I have not had any issues during the 4 years. I had some questions when I signed up and they were answered quickly (within few hours). The 'Beta' sign has been there always, in my opinion it doesn't mean anything. The is a news page, https://news.purelymail.com/ and there are about 5 'items' (mostly some disturbances) per year since 2020. There is a 'free trial' so you have nothing to lose :)
https://purelymail.com/ is brilliant, have been using it for 4 years and am using it with thunderbird and k9.