I have to admit I have never used Didi in China before, but I've been told that apparently I can use a foreign credit card (Visa, MC, AMEX?) in the app. So is it as simple to use as Uber? I'm assuming I can download the app while I'm still in the US, register, add my credit card, and start using it in China? Is it simple and safe to use? Does it avoid the problems with taxis? I can speak Mandarin so I'm not worried about the language barrier. Is it much cheaper than taxi?