You wont actually be able to use them until the mainnet is launched. Buying futures is a risk mentioned above but if you think BCA will be worth more than $42 once the mainnet is launched then go for it. Personally I think the price will continue to go down just like every other fork but who knows. The only good thing I can say about the $42 price on Yobit is their daily volume is less than $50,000 so if it was to get listed on more/bigger exchanges I could defiantly see the price going back above $100.