The pool is called "KnCMiner" which they say has a 1.5% fee. You're supposed to be able to choose the pool even with the inflexible plans but I haven't seen the option.
30% in a DAY? Holy shit. Okay, really didn't see that one coming.
I guess that unless you're betting that BTC will go to $1,000 or something then there's absolutely no reason to pay for miners.
It isn't 30% a day. The difficulty went up 41% today. It changes every 2016 blocks and the time between changes depends on what the total hash rate is over the 2016 blocks.
In a nutshell, 1 GH/s will mine about 0.13 BTC total, so 50 GH/s will mine about 6.5 BTC total. You paid about 12.5 BTC so unless there is a miracle and the difficulty stops rising, you have lost about 6 BTC in the deal.
In $ terms, you paid $1750 to mine $910 worth of bitcoins. It doesn't matter if BTC goes to $1000, because if you just bought the BTC instead of mining it, you still would have come out ahead.
Please note that my calculations assume that the difficulty will rise an average of 20% each period for several months. (it has been rising about 30% per period since February). They also assume that the operator does not charge any fees. For example, Cloudhashing charges a 10% management fee.