I've owned a few 670 models (still own a 670-600) and a couple of 672's. While I like the overall design I found the torsion bar makes the knives hard to open and as a rule remove the bar which turns the thing into a very decent locking liner knife.
Part of the problem with the design is with the bar installed, pushing off with the pointed stud can cause painful thumb tips due to the pressure involved, and found that by removing the bar and adjusting the pivot the knife was a lot easier to open.
Of the two designs, I much prefer the later 672. With the D2 blade and G-10 scales and torsion bar removed, this makes for a very decent EDC knife.
'S far as AO knives go, Benchmade's Nitrous models are a lot easier to operate. Even if the option to disable them isn't built in, the things are so smooth there's really no need, IMO.
Bottom line: Disabled, and torsion bar removed, the 670/672 are good knives for the money.