Regardless of Flask's humble beginnings, it is indeed a serious project, very stable, and quite awesome. And yes, I would recommend it for your use, assuming you want to learn Python as a whole. Flask is easy enough that you can start building an app right away, but at the same time, it leaves out all the extra 'magic' that ship with things like Django, so you'll be learning a lot more Python as you add onto your app. It's a great mix of simplicity and power, and is great for learning. Go for it.