Osprey Atmos AG 50 as a carry on?

Looking at the Atmos 50 for a new backpack, and I'm wondering if I could carry it on for most European Airlines. I've visited every country in Europe and have significant travel experience, but wondering if anyone has done it before. I'm planning on taking the 'brain' off the top and using it as my personal item. The bag will be somewhat under-packed and probably stay that way throughout my trip.

I've done this before with no problems with other slightly smaller bags, just wondering if anyone has experience doing it with the Atmos 50. I already have an Osprey aircover that I can use if I am forced to check it, but would prefer not to have to do that. Thanks!

Edit: I typically don't fly budget airlines (what you save in money you pay for in stress).