Bangle.js 2 Cutting Edge - new heart rate algorithm

Yes, none of those would hurt power consumption any noticeable amount.

Could you explain, option 2, motion value?

We store a movement value for http://www.espruino.com/Reference#l_Bangle_getHealthStatus

But what I'd do is basically just store a running average of acc.diff, and if that went above a certain level we assume there's enough movement that we could switch to running mode