Agreed with the OP... the new design with the ball detent not only cosmetically looks better than on my 4.25" 66 (you wouldn't know it's there until you swing the cylinder out), but yeah, it locks up TIGHT, that cylinder isn't going anywhere once it's in place.
Just picked mine up last evening, and I'm absolutely LOVING it. Fit, finish, and attention to detail makes this the nicest Smith I've picked up in the last few years. Barrel alignment is in perfect harmony with the top strap. Not a single mark on it to be found. I'm really impressed, can't wait to get this to the range for a workout!