Nestbox styles and pros and cons are subject to great debate. While some of the styles below may be easy to clean, they may not desireable from a routine monitoring standpoint.
Fairly obvious what would happen when monitoring this box if there were an active nest inside. If it had TWO openings (one on the side/top, one on the bottom) it might work. This box could be easily cleaned by dumping contents into a bag. Nests should not be dumped on the ground when cleaning boxes, as the debris could attract predators.
There is a hinge on the back of this box. If there were a loose, active nest inside, how would you keep it from falling apart? How can you see the top of the nest to ID or count eggs/nestlings ? If the nest slumps when opened, it will be difficult to re-close the box. It is not very stable, and the hinge can break off when opening.
Obviously eggs or nestlings could fall out of this box when opened.
The student of Nature wonders the more and is astonished the less, the more conversant he becomes with her operations; but of all the perennial miracles she offers to his inspection, perhaps the most worthy of admiration is the development of a plant or of an animal from its embryo.
-Thomas Henry Huxley, British biologist and educator. Reflection #54, Aphorisms and Reflections, selected by Henrietta A. Huxley, Macmillan, 1907.