I used it today and it worked pretty well, far better than a hand pump. I didn't need to clean any full strength dye out of the tap well or running down the keg. I replaced the quick coupler with a different brand because the first one (the one in the pics) leaked. A bonus was that it is easy to rinse out using a CO2 pot.
Cleanup was a piece of cake, no spilled dye, only a bit of green beer. The potential for mess is still there because I still have to open the big 16 oz bottle of coloring and portion it out for each keg.
If I could only find a way to portion small amounts of coloring into the unit without using my syringe it would be completely mess-free. As it is, I still have to pour a little food color into a cup, suck it up with the syringe, and squirt it into the hose.