The instant, yet guaranteed for a brief period trading thing doesn't make sense to me. To my uneducated eye, it seems like either they have to pad the trade like a bookie does, in which case they'll lose business to a real exchange, or they'll lose money from people using that time gap to their advantage.
Can someone explain how it works to me?
The only legitimate way I can understand the feature is if they've decided to open themselves up to a certain amount of losses in order to provide a feature to distinguish themselves in the market. They figure they'll mostly be able to fill with the public order book, and only occasionally have to act as a market maker at relatively recent market price. The idea probably sounded a hell of a lot better to them when they imagined a tight bid/ask. With the spread occasionally sitting dollars apart today on much higher volume than they're used to it's no wonder they're turning it off for a while.