I have had two 640 Pro's, and I would prefer the standard dash 1.
Just personal preference, but I like the barrel and sights better, and I don't use the clips.
Both of my Pro models shot my 135 gr plus P GDSB ammo quite low, and, unlike the dash 1, the front night sight can't be filed down, due to the Tritium capsule being very near the top of the sight. On the other hand, the Pro model is adjustable for windage front and rear. Overkill!
I would prefer that only the front sight be night lighted. I don't think that, during a dark social encounter, I would have the time to line up three lighted dots, which make for poor depth perception.
It's interesting that S&W doesn't offer the standard models without the lock, since they do with the alloy (Airweight) versions. It's an interesting bit of marketing strategy to put an unwanted feature on a product, and then make the customer pay a premium price to buy a model without the "feature"!
Best,
Rick