HR accuracy

What is the general opinion on HR accuracy? During runs, bike rides and just general casual activities? This is my first time with an optical sensor and found the following:
  • Useless for cycling - somewhat correlated but the F5 missed all peaks
  • Running seems somewhat ok - poor tracking within the first 5-7 minutes; much better after that. At times regular and optical track extremely well but the F5 is missing a lot of peaks
  • Average HR on a run has an absolute difference of around 2-3 beats. Not much but the max is off by ten beats
  • Recovery HR after activities is completely off as compared to my F3 paired with the HRM run. Example: F3 read a 30 beat drop, the F5 recorded a 5 beat drop
  • Casual activities seem a bit random - one moment my HR is at 45 reading a book, then 70


I have tried various positions on my wrist. Does not seem to make a huge difference. Just want to get a feeling for how much can be expected from the optical sensor.