Lenny,
Let me preface this by saying I'm in my 60's and the Filson looks to me like elementary school bags (the fancy sort) that came out around the early 1960's - and rather than "retro" I think they look nerdy, as I thought back then. I agree with your assessment - it all turns on the lock. I have handled Filson leather in terms of belts and some of their luggage (canvas with leather trim, etc) and think it is quality, but overpriced (so is Saddleback, but not as much as Filson).
However, so this isn't seen as "Filson bashing" I will also say that their wool jackets are well worth the money, made in the states (Seattle, specifically) from top shelf (not scrap) wool and hold up forever. Best woolen jackets out there...and I hike, do about town, woods walk, etc. all in Filson wool during the winters out here. About five years or so ago, when new management took over, they started taking their clothing production overseas. Sooner or later, the jackets will probably go that route...take a look at them.
Anyway, as a firm point-of-view, I'd say get the Saddleback bag and with that, I will finally end my long-winded post!
Steve