Whatever you get mount it on your helmet so it can be seen above the hood of cars and through their windows. And when you turn your head it will be pointing at what ever car you are looking at.

I noticed a huge difference since putting my flashers (front and rear) up there.

I use a Lezyne 400XL which has a double flash mixer which is plenty bright. It's usb rechargeable and plugs tight in to a usb socket.