I don't think they do anything special. It's just on aggregate between their various interactive mechanisms, there is nice variance to the types of interaction you get to do. Speaking, typing, word selection, etc.
So when you click on a lesson - you like the variance of all the review types before the lesson finishes? That's very doable! Definitely somewhere I'm working towards, and I have a loooot of review ideas XD it'll be a few months until I add more I think though.