The reason I got the cycling specific cape is because it has loops for your hands and a tie string at the back. Neither the front will lift up nor the rear will flap around. I imagine any drug store cape would work if you sat on it in the back and srunched it up under your palms.

This means, however, your freedom of motion is reduced when it comes to your hands. You can probably imagine the cape makes hand signalling not possible, so I use my head to signal when it rains .

The cape sits over your handle bar and may block any handle bar lights. I find this to be fairly easy to adjust though, i.e. put the cape over the light; or install the light lower, i.e. above the wheel. The rear of the cape will probably block any seat post mounted lights, so best to put them behind the rear rack.