Well worth the time
I started learning rails this week. By day I am using Internet tutorials etc but in the evening I wanted an app to help me build my rails knowledge further. I played with this app for 30 mins one night. The next day I was genuinely surprised and very pleased to realise I had new and useful rails commands at the from of my mind. It made my next day twice as productive. I am working now to gain confident mastery of all content in this app. Update 6 months later, still using app for short burst learning when I am away from my work desk, still find new commands I am not aware of or using as I should. Great app, don't think you know rails until you reach mastery of all cards.