Well if you live by the saying - Rather safe than sorry - I guess a extra filter on the plane can't hurt. It probably is much safer too be quite honest...or actually more of a peace of mind story.

I only use a filter when pumping the fuel into the tank from my jug and then have one inside my tank. Too me if dirt comes through two filters then nothing is really going too stop it (once again you do get that odd time probably).

It's up too you, but as was said - it's a cheap insurance but not 100%.