So far, I have not required my students to use Anki outside of class. One of the main reasons is that I cannot yet think of a good way to do it - i.e. accurately assess/monitor if they actually do it.
Soren, an Anki user and advocate, wrote a good article about Anki use cheating and how to stop it that discusses some really interesting ideas.
However, I think there is a larger issue. Most of us use Anki because we really want to learn our subject and know it is very effective. We have positive feelings and associations with Anki.
If we "force" (require) our students to use it AND somehow figure out a way to stop cheating, do we run the risk of alienating our students to Anki, especially to the point where they will not use it in other classes and in the future?
What is more important? Giving the students the opportunity to experience Anki in a way that will lead to some fully embracing it but allowing some to opt out? Or requiring its use, knowing that it is good for them (like vegetables)?
It is kind of a "Is the glass half full or half empty" question.
What do you think?