It's one stop shop for organizing all your emails in different folders, sorting them by date or subject line etc., which makes searching easier so you can find what exactly you are looking for faster than if using other apps like gmail does separately! I would love more customizations - there should be some options that will allow me have my own interface/layout but at this time only basic customization features exist (like changing fonts).
Also sometimes when I open multiple tabs within k-9 app they don't synchronize across devices well unless i close down completely then reopen again later. This happens especially after switching back from work mode where each tab has its workspace set up differently as opposed to home use case where same workspaces appear in every new session. So far haven't found any major issues though we've been testing our business processes over.