Just thinking out aloud, so need to formulate thoughts on this.
3140.hk is the Vanguard ETF for the S&P500 trading in Hong Kong in HKD. It's fees are 0.18% and is subject to 30% withholding on dividend profits. It however doesn't count to any US estate tax liability.
VOO is the Vanguard ETF for the S&P500 trading in the US in USD. Its fees are 0.03% and is subject to 30% withholding on dividend profits. You will however be subject to estate duty after USD60k.
I think, taking into account currency conversion fees direct with bank or broker, up to USD60k its much cheaper buying VOO over 3140.hk.
Seeing as most HK banks do allow for US trading, it may be a better option than 3140.hk (up to USD60k if you care about US estate tax implications).
Any thoughts?