I've had my Fenix 5s since May now and I like it in a lot of ways. My training program consists of running, HIIT, and strength training. In the winter when it's wet, icy or snowy I don't run, I just do the other workouts.
I feel my pulse pounding, but the Garmin just has me in warm up status the entire time. Heart rate really isn't calculated accurately unless I'm running or still. I knew the sensors weren't accurate for weight training going in, but I guess I just thought over time it would improve with new firmware. I also can't wear a chest strap, so that's out.
It's a downer to see my fitness declining when I know I'm training hard.