I have used this lens for quite a while, and I'm very cautious with it. The front element protrudes a lot, and I'm sure it will get scratched if i hit it on something. That's why I always attach the hood between shots, Or keep it in front of me where I can see whats coming towards the lens.
The hood also comes loose quite easily, which is another concern. It is however not as bad as the 15mm prime, which jumped out of its hood while I was hiking and the lens was in my bag, and it landed not entirely strait back on the hood, which resulted in the aluminium hood scratching against the front element for two hours. Luckily enough that was outside of a crop camera frame, so it was still sell-able.
It takes some getting used to, but the routine of detaching an attaching the hood while you move around becomes natural, and really should not be a reason not to buy this awesome lens.
The lens cap and hood are two pieces but I take both off at the same time by twisting off the hood. I don't bother with leaving the hood on only because it can interfere when you want a circular image, and the interface between the cap and hood is not very secure and I'd rather not fumble around clipping the cap to the hood in the field.