I love using Kryolan eye blood for photos! It's easy to use, and creates an awesome creepy effect.
However there are some things that I don't like about this. The effect is very temporary, lasting only a few seconds. So if you're doing a photograph, you have to apply and shoot as fast as humanly possible! Also, I use the black shade, and I find that it can sometimes stain my skin a bluish color where it has been around my eyes and face.
When using this, my vision becomes blurred slightly. Probably because you're sticking a colored fluid in your eyeball. xD
Overall though, this can create some really awesome effects! Especially if you're going for the 'crying blood' look. Would repurchase in other colors for sure!