The lock isn't my favorite, but I do own a Smith & Wesson 637. I've never engaged the lock and I've never had any issues with it.
While I don't discount every story about them locking up unexpectedly, I do believe that it is very, very rare.
They can be removed and you can buy a plug to fill the hole that is left.
Personally, if you like the gun, buy it. You'll likely never have any problems with it.
"He who laughs last, laughs dead." Homer Simpson