Yup, cateyes are great. My Dad is still using the Cateye I bought new like... 15 years ago. I'm currently using my Magellan Explorist 600 on a bike mount, but it has annoyances when used as a bikeputer. It's insanely awesome, but having it plus a cheap cateye would probably the best thing ever.
So that's my recommendation. Get a cheap cateye to keep on there all the time, then get the badass GPS for when you really need to know where you are/are going.