I use the bag 420x280x45 with a laptop in the dimensions. The place is in the bag for more than enough, it fit even more bulky things like power supply or mouse inside. However, these can then be stored on edge in front of the laptop and could cause scratches or the like. Laterally or even separated by the accessory board from the laptop is no more room for it. The many subjects from the Board or the accessory strap I'm not using.
I can not say anything about the long-term durability of carrying strap and zipper, the bag had not been very long and do not use them often.
From my point of view here is very good value for money is given, for me, the investment has paid off, and I can recommend the pocket with a clear conscience.