That depends on how light sensitive you are. If you are slightly sensitive to light, transition sunglasses are dark enough for you to do outdoor activities. But transition glasses won't turn dark indoors and they are not dark enough when in a car, so if you are sensitive to headlights, fluorescent or halogen lighting, transition glasses are not the best choice for you. If you are extremely sensitive to light, you should buy darker sunglasses like super dark sunglasses.
Transition sunglasses, also called photochromic, are sunglasses can react to UV rays. They can change to colored tinted lenses automatically in environment with UV rays and fade away when you go out of UV rays environment. So, transition sunglasses can apply to people who have mild sensitive eye to UV rays. If you have light sensitive eyes, you'd better buy wraparound sunglasses with polarized lenses.