Calf support pedal for Hase bikes

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These pedals with foot fastener and calf supports stop knees buckling inwards when cycling. They really helped my son immensely, enabling him to pedal his bike more easily, less painfully and with more power.
Designed for Hase bikes. They may fit other bikes as the pedal attaches instead of what was an ordinary pedal. But please research this.
From Hase website:
Special Pedals with flexible calf support, adjustable - for shoe sizes from US kids 1/UK kids' 13/EU 32 to US mens 16/UK mens 15.5/EU 52 - max. extension of calf support 46cm to top edge.
Compatible: Kettwiesel ONE, Kettwiesel | Lepus, Kids, Pino, Trigo, Trix
I have a left and right for sale. £290 new each (ridiculous).
Can post at expense of buyer.