First time I post on this forum, so hello to everybody. I'm using my ipad mini to teach English and I'd like to buy the busuu app for $15.99. What I wanted to know is, if I buy this app, is it mine to use forever or is it just for a month use as $15.99 seems to be what people are paying for a premium membership to busuu web-based curriculum for a month on their website? I'd like to know before I give them my credit card details. Thank you for your help.