You can share lessons with your learning peers, friends, or even family at any time.
So no one is left behind, no knowledge is lost: you can progress together, everyone at his/her own pace, effectively.
If you learn new words, you can create your own lessons and share them, of course, so you yourself can help your acquaintances expand their vocabulary!
You are free to choose exactly what words and phrases the app shall teach you and how often you wish to meet them.
You decide when you want to take the exam - but you have to test your knowledge in a time frame at the exam, and you can't skip the exam.
You can learn what you really need, what you really care about - and you can be sure that your knowledge is real.