I don't but curious of what you are getting the lens for? On your D3100 it is going to work like a 42-120mm lens in the FX format. I assume you have a 18-55 that came with your camera. If you are looking for a little more reach for a walk around lens, I would recommend the Nikor 18-105. It will give you more reach in either direction and is a great lens. Another option is to go with the 55-200 or 55-300 Nikor lenses. All have focus motors in them so you will be able to auto focus. Not sure if the Tamron has that or not. Make sure it does if you want to auto focus. The d3100 does not have a focus motor in the body.
I usually try to go with Nikor lenses (they have excellent glass) if I can. Unless it is cost prohibitive or for some reason the OEM glass is rated better, which is seldom the case, I bought a Nikon so I could use Nikon glass.
Just my 2 cents worth.