My previous experience of UORs is that 'kit' bought under a UOR stays on an aircraft for 5-6 years, maybe longer, before the money is found to catch up with the 'training, support, manpower, etc' to support it in the long term!
Items purchased under UORs are often long term requirements, but the UOR approach is a way of finding the money for them and getting them into service quickly.
Whether any/all of this applies in this particular case (Reaper) I am not in a position to say!