One important thing I would like to mention is that Bitcoin price December did not cover the range $25000 - $25500.
May be freebitco.in forgot to add the $500 in the range. Can't blame them since there are so many ranges to cover but still if the price of bitcoin is in between $25,000 - $25,500 then all our bets are lost.
Nice catch! I doubt if it's a mistake. I think Freebitco.in intentionally left that range to significantly increase the house edge. In worst case scenario, the minimum house edge for this event is 9.12% (assuming all bets are made at current odds) or 4.56% (assuming odds are uniformly adjusted with increasing bets). But by removing one range which is closer to the expected price, the house edge further increases. I tried applying Binomial Model and Risk Neutral Method to ascertain the exact edge after accounting the missing range but looks like it isn't possible in case of bitcoin due to unavailability of relevant risk-free rate.
Anyhow, these events must be very lucrative for Freebitco.in.