Hi OP,
black1970 has nailed it. The 3" version of this gun is where the big money is at for this revolver, not the 4" version. However, the pictures shared looks to show the complete package for this desirable 4" gun. So, all comes down to how much you want it. If it was me, I would pass on the $2100 price tag as the 4" guns are typically going for less. If you have $2100 to spend, I would look around at what else once can buy for this kind of money and buy that instead.
So, unless this gun is required by yourself to complete your 686 collection, I would pass.