I've heard of those sprays, but I have read something on Melissa Kaplan's website that got me thinking...
From www.anapsid.org:
Spray Vitamins
Many people ask about the spray vitamins...are they any good? First, we need to separate the two types of vitamin spray products: those that are sprayed on the body, and those that are sprayed on the food.
Body Sprays
Iguanas do not absorb oily vitamins through their skin. When I pointed this out to a Four Paws distributor, whose company makes VitaSpray, she snidely replied that "Pet owners will buy anything that has a picture of their animal on it, whether it is any good or not." So, if you have $8 to throw away, donate it to your local reptile rescue to help feed and heat their needy reptiles.
Food Sprays
The makers of these sprays claim that their product delivers exactly the right amount. The only problem is that no one knows what the right amount is - not for iguanas, not for monitors, not for snakes, not for geckos, not for any reptile. No one has established their daily minimum requirements and, if they did, chances are it would vary greatly from one reptile species to another - what an herbivorous tortoise needs, for example, may differ greatly from what an omnivorous lizard needs. You are not paying for research and longitudinal studies, here. What you are paying for is the pump bottle, pretty label and the nice box it comes packaged in, and a lot of water with a few additives. In my opinion, buying dry powdered vitamins is not only cheaper in the long run, it gives you better control over the amounts you add, and what you provide to your various reptiles.
Hmmmmm....
Veronica