In my experience, they really aren’t. Sure, you need one that’s the right size, that’s a given. Random strong erection might be uncomfortable at first, but as you get used to the cage, they don’t really happen that much any more. And the only real discomfort I ever feel is when I try to ride a bicycle while wearing one because the way you sit on a bike is incompatible with the base ring. But again, as long as it’s properly sized and you’re used to wearing it, a cage is usually only uncomfy due to external influences.