No shields and no cards is an excessively specific state to use a four point card without risk
Reliable, it is not.
Every good player who uses r2d2 shoots to for that! Heck on the falcon with double droids you are actively wanting that situation to happen! with both droids you can not use c3p0 or try and guess 1 to depending on who's rolling what to try and get to 0 shields left with no cards. Any ship that can take c3p0 is better served by taking r2d2 usually. The only ship i wouldnt put r2d2 on is B-wings. Listen to Jeff B talk about it, he's the guy who made r2d2 popular in the first place.