Hi there
Firstly dont rely too much on the calories burned - its a rough estimate only, and each manufacturer uses their own algorithm so its far from accurate - and that's true of ALL makes and they can't give anywhere near accurate date for non-cardio workouts (for the science bit - calories burned are dependant on muscle cell acitivty across the body; this relationship is especially shown up when wearing a HRM for calories counting in anything involving strength such as body combat or pump exercises. The HRM doesnt know if you are using several large muscle groups in unison such as when running or cycling or just a few isloated muscles for example in a bicep curl). Also HRM dont take into account the 'dynamic shift' this is the heart working harder simply due to the amount of err sludge you have generated by working out which appears after a certain amoutn of exercise and is simply the heart/body getting rid of waste you generated and can increase HR by 10-15% toward then end of a workout.
Secondly, the challenge with HRM is design - fitting in so many fucntions but only a few buttons to use. KinetiK are not bad and for the money you get a lot of functions. The HRM requires only limited data - no gender or height. It aslo requires VO2 max - your doc can measure this. When you press set/reset/- to get the calories I think it stops the stopwatch and when you return it starts over and this might give confusing outputs.
Its an excellent tool however for managing heart rate and working in zones so you can manage your exercise. Working 175-190 - thats ok if you are 18 years old (max heart rate is 220 minus your age). Use this tool to manage the intensity of your workouts, varying them between ranges such as 60-70% of HRM for your body combat. There is a difference between exercising and overexertion and using this tool will help avoid this.