If you are familiar with secondstrade it's a the same game and type of gambling. If you are good in predicting prices then go for it but if you aren't better not. But it's not that bad to try it, I've that before but it's quite hard to predict what will be the price of bitcoin for the next minutes.
What OP is saying is that someone can control the bitcoin prices if they have a lot of it, which is easy with just a few hundred bitcoins. The bet is "influence-able", forgive me for the lack of a better term to use. Unlike a dice game where you can don't have any way of changing the outcome no matter what you do.