The only issue I have with the Nitecore D20 is:
Battery: powered by 2 AA batteries (including 1.2V AA rechargeable batteries - NOT LITHIUM-ION
I really like to be able to use lithium AA's. Otherwise, it looks like a good light.
Why not buy your Dad his own light and then get what you really want?
Edit: Hmmm, Does Lithium Ion = Lithium when discussing AA batteries? Is there a lithium Ion AA?