5 stars: Been using the app since last year and now they have a very responsive dedicated development team they have resolved all the issues I've ran into in the past. Features such as read receipts and notifications when a user clicks a link are unheard of in other apps and they continue to add these kind of original features. All while retaining the simple to use, uncluttered user interface. Would recommend, especially the desktop app.
4 stars: It's very good, really like the speed and minimalism. Though there are some minor things that I am still waiting for - like the ability to quickly add a contact to my address book. True inbox was a great idea but I had to turn off in the end, found that I send far too many emails that I don't need to keep in my view.
2 stars: I like the user interface, but honestly have had a ton of issues with bugs and crashes. From a feature perspective, there is really no feature here that you cant get via other apps for free. I tried Newton not for the features but in the hopes that the price would bring a top notch cross-platform experience. Unfortunately, its not been that. Ultimately, this is a good app, but the price is not justifiable.
...