Does the China+ IMSI have roaming capabilities in this region as well? (Can the SIM roam into Vietnam or Japan for example?)
Yes, the Multi IMSI China+ SIM works normally in the other regions. But in Mainland China, just China Telecom the 4G/NB-IOT network is available and in Hong Kong 2G/3G/4G at HKT CSL and in Macau 4G at China Telecom Macau network is available.
1NCE Shop

Buy the 1NCE IoT Lifetime Flat now!

Visit the 1NCE Shop and start connecting your IoT devices easily. Simply order your SIM cards, choose the desired type of SIM card and fill out all required forms. After the payment has been approved you get your cards within two to three business days.