So far, that hasn't been my experience. It'll run fine for 3+ hours with GPS and BT 4.0 connection to the HRM and speed/cadence sensor. It's a 5S, since I was in the upgrade path, but the thing that kills the battery for me has always been running the screen. (So if it's on the bars, that may be bad; I haven't tried that). As to the RFLKT -- by the time you get there, you're probably into low-end Garmin territory anyway. That might be a better route, or a dedicated computer that can upload to Strava and link to an (ANT+) HRM.

I'm with everyone else; if you're going to have an HRM, then be able to see the info. For me, the ability to compare segments on Strava premium is really nice, and probably the reason it's worth it. That and it's 2 cups of coffee a month, so I just cut those out. The HR data is a nice add-on, but I'm not convinced in their zones, suffer score, and so on. It has been a useful tool for me in training, though I don't think it's near as good as power. OTOH, I'm just trying to get in shape to ride a motorbike anyway.