I have a 405 and its pretty functional as a HRM/cycling computer. I often use the oval handlebar adapter when on my road bike and wear it on my wrist on my TT bike. I find that the battery holds a charge for around 5 hours of riding so it's not a working solution if you plan on riding a super long ride. If you don't need the multi-sport versatility consider a cycling specific model like the 500 or 705, their batteries last longer.
One other thing, while I think the numbers are pretty damned accurate at steady speeds I notice a lag when I'm changing speeds, so sometimes it will still read some random mph when I'm standing still, and my cat eye regularly reads higher top speeds for my sprints...