You are in a very similar situation as many people on this forum and after some diligence here is what I would suggest:
1) If you need to keep a bank account in another country than HK, I would suggest to open a HSBC Expat account to invest in UK ETFs (very low fees). You will qualify for Premier everywhere including in HK. The largest benefit by far is the convenience of seeing all of your HSBC accounts and investments in one place (you will see balances of your respective HK + UK + Expat accounts). Global Transfer is also very convenient and slightly cheaper than Transferwise after the FX markup. Besides the convenience, you will also benefit from no fees at any HSBC ATMs worldwide and their free credit card is also decent (partnerships with Michelin star restaurants (buy 1 get 1 free), Cathay vouchers etc. HSBC Premier doesn't really have any other real benefits than this but to me convenience and simplicity is key hence why I will probably proceed with this option.
2) If you only need one bank account in HK, I would open an IB account and invest solely through it. Then you can just stay with Citi, Standard or HSBC for your checking account
EDIT: HSBC Expat also allows you to take a loan to buy property in the UK, which might or might not be useful to you