Actually, UAVs need to be as reliable as a regular aircraft. We often think of suicide drones. But most of those are quite small. Don't think of the shahad or whatever, think of craft like the Reaper. If course a Reaper is quite a large machine with a turboprop capable of carrying missiles, but a lot of UAVs are just for surveillance. Stay aloft for say 6-10 hours. Sending Intel, guiding strikes etc. Then back to base, refuel and off again. They would rack up thousands of hours pretty quickly.
It's made me think these ZD engines are going to be quite reliable. I mean, if you sell dud products to the People's Army...