It's an absolutely amazing app and I definetely recommend it, It's free and you can just play with it and with all of the different languages... it is very easy to use and it will definetely help you achieve a decent level in any language they offer.
It's a good product, but it just didn't work that well for my skin type, It's a bit too drying for me personally, about the effectiveness I'm not really sure, I thought that it gave me even more breakouts, but right now I'm willing to give it another shot. Other people are pretty happy about it so I think I would recommend it just so you can see if it works for you or not, it's not that expensive so that is good.
It's a great product that really helped with my skin, the value is pretty good compared to other masks on the market. I can see that it's pretty gentle and personally I have sensitive skin, I have been using it for a couple of months and I never noticed my skin getting red