Is it really worth investing in high-end heart rate monitoring systems for indoor cycling, or are the free apps that estimate heart rate from cadence and power data good enough for the average rider? Some claim that the accuracy difference is negligible for training purposes, while others swear by the precision of chest straps and armbands. Whats the real-world impact of using estimated heart rate data versus actual heart rate data on training outcomes, and are the benefits of the latter worth the added cost? How much of a difference does it really make in terms of specific training goals, such as increasing endurance or boosting anaerobic capacity?