I used to have one of those. When I went through EMT school and spent a few years actually doing CPR on a (at least) weekly basis, I realized how useless it'd be. CPR tends to force air into the stomach, which results in the patient vomiting. That little shield won't do you much good. The AHA now suggests chest compressions only (no more mouth-to-mouth) for lay rescuers. I've not seen the data, but I've heard that recent studies are showing that very little additional oxygen actually gets delivered to the patient via mouth-to-mouth anyway. Best to just keep what oxygenated blood is still in the body circulating.
To stay on topic - yes, I have a monkey fist or two...