I recently purchased a 4" S&W 686+ for a woods/HD/target/plinking gun and I love this gun. I dithered over whether to get the 4" or 6". My son has a 6" S&W 686 and to me it was just too muzzle heavy. In my hand the 4" is much better balanced. The 4" is also easier to carry and deploy in a woods role when hiking and fishing here in the Wyoming mountains. For me the 4" was the right choice. A curiosity is that with my 686+ I shoot tighter groups one-handed than two-handed.
I always ask if it is okay to dry fire. I haven't been told "no" yet but I don't abuse the permission by dry firing an excessive number of times. I think that if I was told "no" I would respond that I want to try the trigger before I buy and if you won't let me dry fire then I'll have to go somewhere else where they will and spend my money with them.