I have both iOS/Mac versions of the app, and bought it so long ago I’m grandfathered into a semi-premium plan with free cross-platform sync. But for the life of me I can’t use it. There are no subtasks/checklists inside a List; instead you need to either use a special ‘checklist’ type to get a list of subtask checklist items, or you need to convert a task item via “New Checklist From Selection”. That is so clunky. Then there are the weird little things like the “Day After Tomorrow” view that no other task managers use (for good reason, I think). And I don’t have tons of faith in a dev in 2018 who can’t add https to his (extremely slow-running) website - when I visited it after each launch of Chrome I had to manually re-approve it to get to it.
I haven’t found a great cross-platform task manager yet. They all have quirks. But 2Do is a little quirkier than most, and as a one-dev shop changes are limited and they come slowly.