I've now tried that braze-on clamp from Amazon UK (B07T4KTZBD) and agree that it won't work. The problem is that the part holding the rear clamp fixing bolt conflicts with the rear triangle. This prevents the clamp from being placed low enough for the braze-on mount to be at the right level (when I tried the clamp on the bike the braze-on mount is 7cm above the top of the chainring, which looks to be too high). I've now placed an order with Bikegang. I note that the specific Birdy braze-on clamps have the clamp tightening screw placed where it doesn't conflict with the rear triangle. I'll send part B07T4KTZBD back to Amazon.