but ok only 3 stars because of some deductions

First of all must be said that around the ear not heist at Sennheiser that the ear is really completely enclosed. The padding rests on the outer edge of the ear. I personally found a little uncomfortable. Here, the MM400X is much more pleasant. (For MM400X I have written a review)

The operation of the headset is very simple and intuitive.
The sound is better than the MM400X However, the comparison also not entirely justified. The 550X is the latest model with larger speakers and the 400X is smaller and not the latest model.
This for me was not a big decision point but should be mentioned at this point anyway. In sports you can tell anyway if it sounds a little better or not. Finally, you do not listen to sports and music primarily.

For battery life I can not make any statement. Since I tested the headset for a few days.

The weight is not a problem and the headphones well balanced even while jogging.

Everyone wants to hear good music on the road should pick up the 550X.
Each of a small headphone looking for. As for the sport, with the 400X in my opinion better off.