I bought a pretty big laptop recently that is 17.3" in screen size (laptop model is the ASUS G73JW to be exact). This is the bag I decided to buy for it and I haven't regretted my decision for a second. It holds the laptop in one compartment perfectly well with no issues at all. I'm a university student so I carry some folders, pens, papers with me as well and this bag manages all that just fine. If you plan on putting in textbook with it, it may not fit in the laptop compartment, but there is a second compartment. In this second compartment I store the charger for my laptop, which happens to be massive, and again there are no issues in terms of having everything fit.
The shoulder strap is detachable so if you just want to carry the bag around like a briefcase, there will be no problem in doing so. The shoulder strap is pretty comfortable and I've never had any doubt that I might be carrying too much weight in it which could cause the strap to snap off. You can adjust the length of the shoulder strap as well so it fits you perfectly and you can carry it around at the level that you're comfortable with. This is a strong and durable laptop bag/case that is very mobile-friendly.
My one and only complaint with this is that when I'm carrying my laptop around in it, the plastic clips that the shoulder strap attaches to tend to make a squeaking sound. It's not a huge issue but it might be for some people.
Overall, I would recommend this product to anyone that needs a big bag for a big laptop. It will fit just about any laptop just fine, with room to spare for other things you may want to carry around. For a university student like me, you're not going to find a better deal anywhere. For this price, you just can't go wrong!