I personally wouldn't use it.
It is almost impossible to have contact with the horse while using a ported leverage bit such as a kimberwick. As soon as the rider touches the reins, it puts pressure on the mouth, which is normal for any bit. However, a leverage bit also puts pressure on the underside of the jaw, which is basically thin skin and bone. And it also puts pressure directly on the poll, which is, again, thin skin and bone. In most disciplines the rider should establish a contact with the horse. This really can't be done with that kind of bit because contact actually punishes the horse.
Most horses can get used to the pressure and learn to ignore it (in Woodland Eventer's case, apparently). Depending on how often the rider uses the reins, you can actually deaden the horse to pressure applied to the underside of the jaw and/or poll.
I mean, it's basic logic people. You can't deny that the bit works by applying pressure to the mouth, jaw, and poll, regardless of how "gentle" a rider is.
A normal snaffle works on the fleshy part of the mouth only. (Some would argue that broken snaffles put pressure on the roof of the mouth as well but that's another story).
So yeah, please don't use that bit. It doesn't sound like you have enough experience to use it properly. Just go get another snaffle. Try and get a french link instead of a single jointed broken snaffle. They're like $10. I'm sure you can handle it.