The iOS app is not free but was written by the same guy that wrote the desktop version. The Android app is free but was written by others. I have used both and they both work perfectly fine, but like Solution said, you will likely want to do your management tasks on your desktop. The apps are mainly for reviewing. One thing to point out though is that, unlike the desktop version, the apps do not sync automatically (which makes sense if you think about it) so you need to make sure Tokyo sync when you are done studying. As far as cost, I’d say 20$ is not too much to pay, especially if you’ve already gotten years of use out of the free desktop version.