I've tried a cape, but found it to be a nightmare. I like clean and open, and prefer things that fit closely to my body. I tried riding with a rain cape as a storm was blowing in, and the "sail" effect was downright dangerous. Even without wind, I could feel the resistance when I rode. Not my style. I really wanted to like it, as I know they are very effective for rain, but there were too many downsides for me.
NB : the one Grant & Co. got Grundens to make is heavy Duty stuff, being a heavyer thick fabric It doesnt Blow around as much..
Added Benefit I dont have the wet soaked through Gloves. as they are under the front of the cape, and the awning formed by my outstretch arms means no need for rain pants.