I can attest to the steel disconnector units not always having "perfect" dimensions... a 639 that I still have gave me fits until I figured out what the issue was. The disconnector itself had a rough edge and it would catch on the edge and stay UP, locking the slide open in the middle of a magazine.

At first I figure it was my thumb inadvertently hitting the slide stop -- but holding the pistol with the slide locked open, the magazine half full and the slide stop DOWN had me thoroughly mystified for a long stretch on that range day until I was able to replicate the problem at home.

This was a 2nd Gen. Neat guns and the link between where it all started and the pinnacle of the design, but still the red headed stepchild in the Three Generations of the S&W pistol.

As for another good upgrade of the TSW (as much as I hate to admit! ) there are some subtle ergonomic improvements also, a big one for me is that they did more detail rounding and de-horning where the bottom of the trigger guard meets the front of the grip.

Like the BIG upgrade from 2nd to 3rd Gen, S&W made this area even a bit better for a more comfortable, secure hold on the pistol.