Has anyone tried this?

http://suuntowatches.com/t6.htm

I'm considering buying it for my engineer husband (read: info geek) but haven't heard of this before. Can oxygen consumption, etc really be measured by a HRM? My guess is no, it can only estimate it based on general data and therefore isn't that accurate. It also doesn't say that it's waterproof or water resistant; I'd hate for a downpour to ruin it - it's not cheap. Any feedback?