I’ve started using my Jingda “leather” iron again after all. Having ground and filed the bottom flat and the width down to 24mm, it really is quite good. The minimal temperature drift and massive heat retention is excellent. As for the shoe on mine bubbling, it has to be poor metallurgy. I have to assume that it’s made from recycled alloys, and they left impurities in. Different batches will have different levels of impurity.