I've thought of a few design flaws.
1) What about hairs when you take the thing off. Maybe if i was Max Mosely but that sounds to painfull for me.
2) Where does the "man seed" go? at least with normal condoms you get the bulb at the end but with a spray on one theres no where for it to go!!! Messy.
3) What about the idiots who are going to spray rubber on other places? You know they're out there. You probably know someone who would. Imagine trying to explain it to the doctor in the Emergancy Room. "I must have left the can on the chair and when i sat down naked it just went off!!"