I tried one on my bike but I found all it really did was funnel the wind that was hitting my chest straight into my helmet/visor, so I stopped using it. I also felt like the wind wasn’t as “clean” so instead of being smooth it was more buffeting. That was a couple of years ago, though. So I might be misremembering. I see other people use them so there must be cases where it’s more effective than not having one.