Further to my review below, I eventually got this working after downloading from a different source.
I really want to like this app. It's very straightforward, virtually no learning curve and that's great. However, if I may make 2 suggestions.
1. It's very 'clunky,' especially with long documents. The writing and editing experience could be a lot smoother and more responsive.
2. I'm not American and don't write in English (United States). However, the app seems to auto-switch back to this default setting. So when choosing my default language--English (United Kingdom)--I want the document preferences to remember this.