That is cool that it works offline. I will not use it because I don't like the voices. The free meditation app I would recommend is the Healthy Minds program[1]. I have also seen Medito recommended, but the thing that I like about the HM Program is that it is a very straight curriculum, instead of various options scattered as options.
This is great! I've been using Headspace, but recently I get a Duolingo vibe of it. It's still good, but Healthy Minds is in other league. Thank you!