In theory, one freewheeling device would have to engage, then the other. Making the over all effective engagement points feel like you have something like 10-15. But in reality, what will happen is one free wheeling device will stay put, and only one will spin. So, it might not make much of a difference, it certainly isn't advisable though not only becuase of the extra weight, but becuase of the fact that this is trials where you're moving the cranks in both directions both freewheeling devices can become unengaged and that could happen when you're doing a gap, suddenly you'll need to turn the cranks twice as much, and i'll probably end up making you eat the wall your gapping to.