What's the difference between the Fisheye 550 and the 590

No difference. According to the query fish leap official website, fish leap 550 and 590 both for intelligent free code blood glucose meter, its function is the same, so there is no difference. The full name of Yueyue Medical is Jiangsu Yueyue Medical Equipment Co., Ltd, the vice president of China's medical equipment industry, formerly known as Jiangsu Yueyue Medical Equipment Co.