You get a very bright afterimage, but I simply refuse to believe that any harm can come from staring at the sun for 15 seconds. Having said that, it is silly to look at the diamond ring before totality because it messes up your night vision. They fit over regular eyeglasses and allow very little direct sunlight to reach the eye. However, I felt no problem at looking at the diamond ring at Aruba following totality for 10 sec or so, with the naked eye. Having said, that, I would not publish the above as advice to the general public.
Partial phases are uninteresting compared to totality.
They are either safe, or not safe. And I understand from Chou's work that, in theory, one can observe the sun for an umlimited amount of time with such glasses without any damage. Whether it is desireable, or the usual practice for experienced eclipse observers, is another issue. Bob Morris, Prof of Engineering. If in doubt - don't look.