This is true about how you overall adjust to the weight of the way the stainless, where you wouldn't even notice it anymore. On the fitness side of things in the gym, Let me tell you was an avid weightlifter based on my experience , I caution the sake of wearing the stainless model around weights and machines, as it can easily dent the 316 L stainless casing (Being it's a very soft metal).
Where as the aluminum holds up really well in the gym and the Times I hit it against weights, it didn't even scratch or dent the aluminum. So both models have their advantages for fitness, depending on how you use it. So for Gym purposes, I prefer the aluminum model.