I used a paid Android app (https://play.google.com/store/apps/details?id=org.hamstudy.mobile). The interface was non-distracting, it's up-to-date with the current question banks, and it has a few modes of operation I find useful, like homing in on areas I was weak in. Nicest to me was an "I don't know" answer button to avoid the accidental negative training of having to guess and program a wrong answer in your memory. There's also an "Explain" button that gives a pretty good summary of the correct answer theory, at least enough to research it further. I can't objectively say it's all you need. I wanted to be a ham as a kid and read everything I could get my hands on. Amazingly a lot of that is still in my head. I went to test for Technician and passed the General thanks to it. But using this app was pretty much all I did to pass Extra.