Realistically, I don't imagine any of those amplified ear devices working very well. Its worth a shot if your on a budget, but all it does is amplify sound that you hear anyhow, ie. it amplifies everything, it has no selecivity.
What is more suitable is a shotgun mic or a parabolic dish microphone, as these are directional and will pick up only in the direction they are aimed. A parabolic mic can be made from an ordinary elecret by adding a dish, apparently those domed mirrors work well. They aren't too inconspicuous though.