Investing 0.1 in your own busniss and try to earn 100 btc is a dream and if you invest in someone else busniss and risk them is not a good idea you need to work with your own money not give them and risk for a scam
Their is no point when you know winner would be just 1 and not many and out of thousand of entry if you see % it is negligible . Hence probability of you winning is not much to risk those 0.1 btc. Instead I am sure if I invest now this in some coins as market is down I would get much better returns and can easily double in coming month mostly.
Thats right its not worthy to risk your money in lotteries with a bit chance for you to win. For sure 99.9% you wont be selected to those winners and just like what you have said it would be better to invest in coins that is in dips now or in promising ICO's that are likely to succeed rather than risk your money for nothing. Investing is more realistic and has a possibilites of good return.