I was surprised to see them dropping in the fleet missions and in the Tholian area. I preferred them as rewards for STFs, aka the mystery box reward. They look horrible as a drop in space or on the ground. Keep them as end missions rewards, not constant drops.
I don't like lockboxes much but I actually got excited when I realized on tribble I had more then enough points to get lots of master keys for the collection I had built up and happened to have had transferred with my character. Unfortunatly they don't seem to sell the keys in tribble for the lockboxes that are dropping... at least not that I've seen.