Indirect from the UK

Hi, I have found flights from the U.K. to China and want to check it is eligible for the 144 hour free transit. I have a UK passport and will change aircraft in Helsinki. I plan in Nanjing/Shanghai for 5 nights. Flight 2 is a separate booking with a different airline.

Does it matter I am flying indirect from the U.K. and will change aircraft in Helsinki? Does that matter or will the confirmation be enough to meet the visa requirements?

As a Brit I don’t need a visa for Hong Kong, more the Nanjing/Shanghai part I am worried about.

Flight 1. London - Helskini - Nanjing
Flight 2. Shanghai - Ho Chi Minh City
Flight 3. Ho Chi Minh - Hong Kong
Flight 4. Hong Kong - Helsinki - London

Any advise is appreciated.
Thanks, Danny