I cannot speak to things like half-helmets that leave so much of your head exposed, but I can speak to full-face helmets vs modulars: Once you've used a modular you'll never want to go back to a standard helmet. The convenience of being able to keep your helmet on yet being able to talk, eat, drink and see more widely during breaks cannot be overstated. As for safety, virtually every major helmet manufacturer has embraced the concept, and many have DOT and/or SNELL ratings.

There's been some good discussion here in MCM and elsewhere about the relative merits of paying more for a helmet, particularly those costing north of US$400. The general consensus has been that the difference between "helmet" and "no helmet" is far vaster than the difference between "cheap helmet" and "expensive helmet." Expensive usually means quieter, more comfortable, more features; whether it means greater safety is a question of some contention. Your brain is basically a big soft sloppy mush, and no shell no matter how expensive will prevent it from getting severely jostled and rammed up against the inside of your skull when your head goes from 60 to zero in an instant. But in a slide, or a glancing blow, or the kind of hit that comes when the bike comes out from under you, almost any helmet protects your head far, far better than no helmet at all. In all of my getoffs, most of them benign but a few of them rather violent, I've always been grateful to have been wearing a full-face modular.

So this question of "good quality" in a helmet is a lot more complicated than merely a discussion of price or features.

cheers!
euphonius