What do you like best?
The best thing about iA Writer is the interface, which is minimal. You don't need to worry about font size, or colors, or alignment, or any other visual aspect you might think, you just have to focus in your writing. This software uses Markdown, a simple text markup, to create the necessary hierarchy and give the appropriate importance for certain words, using titles, bold and italic. It will also give you a preview, so you get the chance to peak how it's going to look.
What do you dislike?
The things I don't like about this software, is that you need to pay separate from Desktop and Mobile, and you won't get free major updates, for example from version 2 to version 3. But that's a business model like everything else. It makes sense to be this way, if you think how much effort and thinking it's put into it.
Recommendations to others considering the product
If you like to write or take notes, and think that your current software distracts you from getting things done, you might consider giving iA Writer a shot. It's not an expensive software, will run smoothly in your machine and probably help you in your daily tasks.
What business problems are you solving with the product? What benefits have you realized?
Daily routine of taking notes, writing articles about the work and organizing research by topics and links. It's clear to me that having almost no interface in a writing software, helps you concentrate in what really matters in that moment. You will get more things done by using it!