It might be worth cashing out some of your tokens just in case. (Cash out enough to cover your initial investment).
Their system sounds unsustainable - it's probably a loss leader to attract customers. Loss leaders work if you as an exchange earn enough later to cover them. If you don't you end up going bust.
It is not unsustainable. They share 100% of fee earnings but they are holding many ONE Tokens so they are getting dividends like every other ONE Token holder. That is brilliant and fair in my opinion...