Yea the subscription price is a bit steep for something that is only an email client. For me I subscribe to Office 365, which includes MS Outlook + 1TB cloud storage for not that much more per year than what Newton costs.
Alto is an interesting client, the file and photos stack are quite useful features if you're the type of person who always refers back to emails to find attachments.
Was a great supporter of this app until it required a paid subscription to use their main features. Still a great app in general, but personally didn't think it was worth the cost for an app such as this.
I now use a similar free app called Alto which is surprisingly made by AOL. Good interface and functionality, though not a seamless experience as Newton.
After a several months long closed beta test, CloudMagic has released their Newton email client for Windows 10 via the Windows Store. Newton has some powerful email features, but costs US$50 per year and is competing against paid and free stalwarts such as Microsoft Outlook, Mozilla Thunderbird, and integrated OS clients.