I've got its brother, the 640, with the same 2.125" barrel. That extra quarter inch of barrel over the 442/642 helps the .357 round along a little bit, but these guns still don't get the full measure from the .357 round -- and thus there tends to be a lot of blast in that caliber.
If you like J frames, the 640 and 649 are great exemplars of the type. At 23 ounces, they are heavier than the 15 ounce 442/642, and that dampens recoil a bit. That extra weight can make them a little heavy for pocket carry -- something to consider.
The hammer on the 649 gives you SA, which is missing from the 640 (and 442/642). Some will argue the SA capability of the 649 is wasted in a gun intended for close-in use, but it might be of value in some situations.
I've always wondered if the 649 accumulates dirt and pocket lint in the open channel above the hammer. Someone who has one might comment.
And the 649 is iconic -- it was shown in perhaps the most famous picture of the Vietnam war, in which General Loan used one to shoot a Viet Cong prisoner who had just butchered the family of one of Loan's officers (Feb. 1, 1968). That picture did a lot to discredit the South Vietnamese, our allies, although summary execution of an illegal combatant is allowed by the Geneva Convention (but that's another story for another thread).
Saigon execution: Murder of a Vietcong by Saigon Police Chief, 1968 Opinions on its appearance (the hump) varies, I guess, but I'd take one in a minute.