i just use duolingo on my iphone but it doesnt matter what it is on. it still rocks!
It is fun on either platform be it on ios, android or computer based (I also use it on my iphone :D)
Awesome, but if you are not using the website, remember to come here if you ever get stuck in a section. The sentence discussion area of DL (not currently available for iOS) is a great resource if you are having trouble understanding a concept.