If you are looking to buy a 686, get one made before 2000 - this is when the locks were "deployed" - it wasn't a decision S&W made freely - they were blackmailed into it by the Clinton Justice Department in exchange for dropping a bundle of "unsafe product" lawsuits (not really unsafe, just the old "it kills therefore it's not safe" kinda lawsuits anti-gunners tried). S&W was the main target, so they bore the brunt of the lawsuits. The gun came out in 1980, so there's 20 years worth on the used market without the lock - I saw 30 or maybe more on gunbroker the other day. I have a 1985 model myself.
It is a shame that the Clinton admin. did this, but we have to live with it.
the lock is also very easy to disable if you have a flat blade screwdriver, some mechanical ability, a file or dremel tool, and about 1/2 hour. Instructions are widely available at the smith-wessonforum.com
I would prefer a pre-lock gun. Should I get a better deal on a post-lock gun, I'd take it and then immediately remove the lock mechanism, and then not worry again.
Hope this helps.