Given the choice of new or used for the same price, I'd go new every time. Why buy 'someone else's problems' when you can have something protected by a lifetime warranty? Factor in the ten shot cylinder, and it's really a no brainer. As to internal lockwork, it's essentially the same. The MIM parts may look different from CCH parts, but they have proven to be far more uniform and precise and just as strong, while the frame mounted firing pin is also an improvement. The IL is a non-issue to me - most of my S&W revolvers have them - and I've had zero problems with them. My EDC CCW, a 642-2, even has one - so I am betting my life on one. Simply not a problem.
Yesterday at the range, I shot only my new 4" 617 X10 and 5" 63, my longtime favorite 625MG in .45 Colt came home 'clean'. I saw a range friend who told me he had just taken my advice - and bought a new 617 - and loved it. Shooting mine had sold him. To be blunt, we are both 'over the hill' - and made the move to a 617 a bit late - but made it nonetheless. It's a great purchase - I just prefer new - especially at or nearly the same price. Congratulations - either way!
Stainz