The Model 40 and 640 are fine weapons and basicly modified Chiefs specials,
All J frame models have different advantages/disadvantages,
The Model 40 disadvantages are you cant cock the hammer for a single action aimed shot, (some might argue why are you taking an aimed shot in SA self defense) and the weight of a steel framed handgun.
The advantages are no snag when drawn from CCW carry, no hammer opening for dirt and lint to enter the action and a far less greater chance of accidental discharge .
The weight can be overcome with the Airweight version Model 42,
If more corrosion resistance is required there is the SS Model 640.