As I wrote
earlier, with the current system, it is still profitable BUT it is not that interesting. Why?
First, let's look the table (it is a clickable image that will send you to the actual spreasheet, that you can copy with
File, Create a copy to play with):
Because what you earn with a reasonable time per day (10 hours) covers just a bit more than reinvestment. For example with level 2, you are playing 10 hours a day for almost a month for... 0.02 BTC - 4 euros (0.05 of reinvestment + 0.02 of net margin, not counting time and energy spent)
As far as investing goes, the safest strategy (apart from not investing) is to wait till you quadruple the reward then upgrade the level
Say you are level 2 (0.05 BTC). You wait until you get 0.2 BTC then upgrade. 0.2 BTC means you achieved ROI (0.05), have enough to buy level 3 (0.1 BTC) and still made some profit in case it goes bust after you bought level 3 (0.05 BTC).
Now, considering you earn only 0.02 BTC per 19 days, to reach your goal you would need 190 days of playing - more than 6 months.
Yeah, you read it right: the always-profitable strategy requires you to play for six months in a row, just for one level - except if the admin is Bernard Madoff, the site will have stopped long before that. And good luck finding referals of the same level than you (less than your level, they are negligeable).
If you want to avoid losing money without the security of getting some when it will go poof, you can aim for "just" three times your investment. So, for level 2, this means 0.15 BTC. Instead of six months, you'll need "only" 152 days, five months.
So lets's sum it up
If you invest, you need to play 10 hours a day (including weekend) for two weeks just to get your money back
If you want to increase level, you need to do it for 5 months
If you want to increase level and get some money back because the site can go poof anytime, you need to do it for 6 months
Math is hard, hey?
) 
