Anyone used these? They look interesting and I am consideringtrying them.

Here is the link to their website:

http://www.starrflight.com/

Are they gonna go through a deer? What happens when they get that far??

They will definitely not go through a deer. That's actually one of the nice features, though. When the arrow contacts the deer, the fob will fall off and mark the point of impact, making it easier to find the start of the blood trail and also increasing likelihood of the arrow passing through (smooth shaft instead of vanes). Never tried them, but that's how I understand they would work.