This app isn't really free. As far as I read, pricing is: up to 60MB of editing files per month is free (that's a lot of text, but with embedded pictures it isn't). 1GB of editing costs 3.99$/month, resp. 39.99$/year. Unlimited usage of the app costs 5.99$/month, resp. 59.99$/year.
I'd find it practical if the pricing for such rental/sign-up/freemium/free-to-play-apps would be written in the app's description. Of course, "free" reads great –but even on Polaris' website it's really hard to find the pricing. Probably they want to avoid a direct comparison with Office365 – which really costs about the same for unlimited use…