I set it for five second recording for hiking to get better battery life. The accuracy was okay; it would cut every switchback but for most people hiking at a slow pace it would be fine. I would never use 5 second for running, cycling, mountain biking, etc. You need "best" for running or cycling and even "best" is not great. If you want good instant pace, use a footpod like stryd.

The real battery suck with the spartan trainer was the wrist HR, which didn't really work for me anyway.

No kidding. On every single run the measured HR hit ~ 220 bpm within the first minute and stuck there for the duration. FWIW, it didn't have any problems on the bike.

What kind of battery life are you getting out of one charge?, Long enough for IM or not even close? What if you turn off the wrist HR? I have seen it in Amazon for $210 and I am tempted to give it a try.

Not even close for a full IM.

The polar vantage watches will do a full IM, otherwise 935/fenix series/suunto 9.

What about a half IM? 6 or 7 hours in multisport?

I got 7 something hours of hiking with a chest HRM strap, optical HRM off, gps set to high, no other bluetooth connections. So for a HIM you might be okay, or not.

Or just get a new vantage or a fenix 3 refurbished for the same price (or even a refurb 920xt) and don't worry about battery life. I just made this decision a couple months ago; pm me for a detailed comparison.