Reverse lens macro, like most experimental techniques I try out, is extremely tedious.

The depth of field is terrible, you need extremely bright light, and breathing will throw the entire image out of focus.

I can't explain the science behind it, but turning your lens around like this makes the focal distance unbelievably short. Depending on the focal length of my lens, I am typically anywhere between 1 - 3 inches away from the subject. Breathing is a big no-no, because your focal plane ceases to exist if you move more than half a centimeter away from your lens' ideal focal distance (no autofocus here).

And because you're so close to the subject, there is almost no room for light to actually make it to your camera's sensor. It's full, bright sun, or studio lights if you have them (I don't).

Oh right, you also have to manually hold the little tiny metal aperture lever on the lens open. Say goodbye to f2.8 and hello to ambiguity. This is both how you choose your depth of field, and how you manage your light levels.