How much study has been given to its statistical effectiveness?
Zero. Could you imagine trying to run an experiment to prove its effectiveness? Two people go in the water, one with regular wetsuit and one with shark repellent wetsuit. Both come out alive, neither even see a shark.
Repeat every day until one gets attacked (would probably take 50 years.) Then repeat until enough attacks have happened to create meaningful statistics (500 years?)
Sharks really don't care what we wear (or don't wear...), they're just not interested in us. It's always funny how people react when I tell them we dive with GW's off of southern California. The look of mild shock and confusion ("are you crazy? how did you survive??") is priceless. Especially when I follow up with "well, of course there's a lot of them in the water with us... but we never see them."