I can call you Betty, and Betty when you call me, you can call me Al.
As is the Model 442, the 638 is an aluminum frame S&W Airweight; cylinder, barrel, and crane are carbon steel on the 442 and stainless on the 638. Will the 638 replace the 442 as my preferred pocket revolver? I dunno; I have not had a chance to take her to the range yet. Also, this is my first revolver with Crimson Trace laser grips. I was into laser grips when they first became available and became disillusioned early on. Crimson Trace has a great reputation; I may just become a believer.
J-Frame convertible IWB / Pocket holster by Matt Del Fatti. This is the only IWB revolver holster design that works for me.
Nutnfancy does a fantastic review of an identical (other than the lock) S&W Model 638, including the use of laser grips (same manufacturer, different model).