I only use the iPad version of this app. It's pretty nice. It would probably require extra study. I would use this app as a supplement to learning. But it will help you quickly catch on to grammar and learn the language more "naturally," or how a child would.
My main complaint, however, is that purchasing the lessons on one device does not give you the lessons on your other device. I must purchase all lessons once on my iPad ($4) and then again on my iPhone ($3). This needs to be fixed. Until then, I refuse to purchase the lessons twice, and I stick solely to my iPad. If this were not an issue, I'd rate the app 4 stars.