FWIW, I've got Cateye Astrales on my bikes.
Never had a problem with a leak on a Cateye. Maybe there are other brands that can say the same, but once I found Cateye really knows how to keep the water out, my brand pilgramage stopped. Sometimes the contacts short out in heavy rains, but this can be mitigated with Vaseline or Chapstick on the contacts.
Cadence, useful two ways. First, make sure you're not busting your knees by keeping the cadence up, especially as the day wears on and the road turns up. Second, set the display to cadence and distance. One is meaningless (except as noted above), the other is useful for following directions but changes so slowly you don't watch it. Seeing my speed while riding was usually depressing, and I could always check the max speed later after a downhill -- it takes too much concentration to stay up and on the road when you're over 35 mph to watch the speed display. That gives you a chance to see the scenery, and watch for traffic, since the electronic gadget isn't really all that interesting.
Wired, so there's only one battery to worry about, and it'll usually last me 18-24 months.