I’ve done this. it cost 1000Hkd (3-4 years ago) to transfer into HSBC overseas securities account. you cannot transfer out after that (say to avoid trading at their ridiculous commissions) other than if you’re closing the account. even then it’ll cost you 1200hkd/stock
to me, anyone who already uses hsbc expat investdirect has no need for the hsbc overseas securities account. i've closed mine.