They drop them 80% of the time? That's pretty good.
Considering even granite crabs only give 21 exp, that's not really that good at all. At that rate, we're looking at a skill that's twice as slow to train than RuneCrafting. Yeah there are pouches that get great exp at higher levels, but require charms that seem to be very uncommon drops. If you look at all the inv pics of people hunting for them, you'll see quite a few (though still only worth one trip to the obelisk...) gold charms and like one of each of the others.
Ok that's enough of the granite crabs, there are way better summons so 1 charm will be worth like 400-500 exp