I am in Shanghai right now. Alipay is pretty legit. I am using the Tour Pass, and its linked to a Capital One 360 debit card. (Mastercard logo).

I can add funds instantly to my Tourpass. Scanning QR codes works, as does having my QR code scanned.
Its pretty seamless. I do have cell connectivity via TMobile, and its a bit slow sometimes, but I would say 95% success rate. If you dont have cell service, forget it.

Almost all vendors take AliPay. The small drink cart guy, big chain stores and restaurants, the vendors at the knockoff market.

Overall, its super easy, and you don't have to deal with carrying cash, which is nice.