Answering you: This is not a scam, this is an original way of doing Bounty, please do read what we have under the slides on our ANN.
If you join 1 day before payment due, you will get paid based on what you have done 10 posts full payment, 3 posts 1/3 of the payment.
Ok, but I don't understand how do you know you will have enough BTC to pay everyone if there is no limit of people joining until the 15th of december? we are at 55 pages of people joining already, at these rates and at this pace is going to be a lot of BTC to pay..
also notice I did a mistake and entered activity points as number of posts, edited it.