Be careful who you are actually dealing with here.
You are not working for NATS.
This is a sleight of hand by the HK Civil Aviation Department (who is under the most dysfunctional Bureau in the HK Govt- the Transport and Housing Bureau THB ; otherwise known as SADIM. The opposite of MIDAS- everything they touch turns to Sh1t. Google HK housing, High Speed Train etc...).
Despite the Govt just posted a budget surplus of almost HKD 100 billion, they can’t find the funds to properly let the CAD to employ additional staff.
So they instead tell the Airport Authority to fund the extra controllers.
The AA is not stupid and can see the legal wrangle they can end up with so Farm it out to a third party NATS.
Despite the government wants to distance itself from all this, make no mistake, it will be the CAD who is calling the shots on what your roster will be, when you can have leave and who you will answer to.
They’re a crafty lot.
You have been warned.