Both the Airaid Jr and truflow should be vacuum formed plastic tubes, so convection should still be at a minimum. However chrome tubes reflect plenty of heat, so I haven't heard/read a decent argument for either material.

If your Jr kit is just the MIT, I don't think you'll notice any change in noise since the filter is still baffled. Between the two, I'd pick the truflow, it comes with more parts. I doubt you'll notice any change in mileage, maybe a couple of miles per fill up, but a full MPG would be a little much to expect.