Actually, I've been using the web site this week on the Nokia 1520. It's been more reliable than the app in my opinion. Every time I've tried to do anything with FP+ and the app, I get the "We can't complete your request at this time" error (at least 8 out of every 10 times). I haven't had that issue using the site on my Windows phone.
I would not hold my breath for any Windows phone app soon. Maybe in the future. Right now it is designed for the one and two most common OS's, Android and iOS. Access to the website works pretty well.