the risk of impaction is there but it is not a big risk. You have to understand many frogs are by nature designed to eat prey of such sizes. The largest problem you face by feeding a small frog such big prey is the insect starting to rot in the frogs stomach before it can digest it, producing deadly bacteria that will cause the build up of gasses. The sign is that they will bloat. you can tell the difference between a frog with a full tummy and bloating. This is also common in snakes as well. not only will large prey cause this but as well as feeding them to much smaller prey. Unfortunately this has happened to one of my frogs a few years back and it is a lesson well learned.