What’s the shelf life/expiry on the control solution like?
I see it’s only one, whereas a unit like the Lactate Plus as two solutions (1 for low-level calibration, 2 for high-level calibration). LP’s shelf life is 3 months after opening the solution bottle.
Haven’t used a calibration solution yet, only the calibration strip that is included.
I see the Edge is available locally, for me, which is great for ordering the consumables (strips and solution). The import process is too long and can be expensive.
The problem living at the tip of Africa… 
I agree with everything said here about graphs shouldn’t match up and on using multiple parameters to triangulate.
My 2c as to which to mostly look at - it depends on the goal of the workout.
For an endurance session I prefer HR because it is a better indicator of how my body is doing on that specific day. If I stick to power number, on days when I am carrying fatigue, stress, etc., I may be in z3 rather than z2.
But when doing more top-end work (tempo/sweet spot/threshold/vo2), I focus more on power. I’m less concerned about the zones and more about getting the work in.