Didi is "hailed" via APP just like Uber, and needs either Wechat or a dedicated app. English language interface available, and can link to foreign CC. Can also use to hail conventional taxi.

Black cabs are informal taxis, and can't be hailed...you flag them down on the street. I suspect a lot of them are now Didi drivers! We still see our regulars in the neighbourhood, but don't tend to call on them anymore...but since they are around, presumably they still have plenty of clientele! I have used "black cabs" many, many times without issue: the only critical piece of advice is that it's essential to negotiate and agree a price upfront. For Didi, it's calculated automatically, so that's not an issue.

tb