Ok, I have solved for me at least the problem of the heart rate readings. I have no idea why this works but it is now consistently within a few beats of my Polar cheststrap while cycling. It isn't able to keep up with rapid changes ie recovery from 190 to 110 in 90 seconds or rapid increase on a climb...but over a ride the chart tracks the polar aside these gaps and the average is now within a beat or two. Plus calorie count is within 2 or 3 % over a 90 minute ride. Thats good enough for a wrist based device and the gps tracks well.
What did I do? Swapped wrists and tightened the strap to very tight. Also clean off the leds and wrist before an activity.
I still don't think its any good for HIIT but for my main activity of cycling or walking I have solved it.
Problem is my strap is failing again. I have super glued it and it is currently holding. I'm loathe to take the 25% offer as in the UK it is now £160 on the high st. Also the model is getting on a bit and other brands are surpassing it.
Hopefully a new version is coming soon, it would be useful to know.
