The latest development in my crank saga:
It seems the extra leverage of the extender, plus my fat ass, was too much for the aluminium in this $50 crank. Checking my eBay history, I bought that in Jul 2019, so it lasted a little more than 2 years. Not very impressive.
I've been fine without the left pedal extender, but my right foot is more twisted than my left, ditching the right one would be annoying. I see on eBay I can buy a 16mm extender instead of the 20 that's on there now. And I'll try to put my old Mr Whirly back on, hopefully that's more durable