Well I don't think bitcoin is any more stable than it was a year ago (pretty sure a year ago it was more stable when it was around 5 dollars compared to today's 10% swaying every day.), but besides that, bitcoin charges a fairly large fee for microtransactions. As an example, I was trying to transfer teh US equivalent of $1.07, and I got charged 10 cents extra. Lickewise, when I tried transferring something larger, like $1.68 (sorry I don't have much on me right now), I was charged 12 cents. Since most osu! transactions fall under the micro-transaction category, I have a feeling that it might just be cheaper to use a normal credit card.
Besides that, why Bitcoin and not another cryto currency, besides the fact that Bitcoin is the defacto standard these days.
