Powercal doesn’t use calibration for subject. They tried but found it added no additional accuracy. It sends to ANT+ signals; HR and power, and you can deconvolve power to reconstruct the algorithm (or a rough version of it). I don’t know which algorithm Strava uses for HR.
I bought my Stages in the US just as they were launched. Stages have been absolutely faultless in supporting their product, despite two failures, and have sent me replacements immediately. Give a few bike shops a call and ask hem to order you one for collection.
EDIT
does the Powercal tell you anything about your effort that you couldn’t have gained directly from HR
It tells me I’ve stopped at traffic lights 😉
More seriously, it gives me a reasonable 30 sec average power that I have used when on other bikes to fill in data and monitor Normalized Power. It’s not going to help with 3sec sprinting efforts.