OK, the OP asked best for the $$.

Is the Polar utterly useless crap? At 1/3 to 1/4 the cost, from what I've seen it is ~10% accurate compared to 1-3%. If the error is relative (i.e. always off but repeatably), how can that NOT be the best cost/performance option? Is the exact wattage key, or fairly accurate, though not exact, power trends?