IBHK is the broker i use and I am happy to recommend, PM me for referral link if you want which would give us both some bonus. I have no experience with Schwab, but one small piece of information to note, IBHK will pay you 4.33% on any unused USD funds in your account, whereas Schwab will pay you only 0.45%. What I mean is just transfer your HKD to IB, convert it to USD ready for investing, but then if you dont invest and just leave it sitting there they pay you 4.33%. So already you are winning just opening an account and transferring some money in.
For more advanced investing and leveraging, IBHK also offers the best margin rates. For example, you can transfer HK$1000 into your account, then buy $5000 worth of stocks, you have just leveraged 5 times and you have taken out a $4000 loan with IB! This is all automatic and seamless, gives you 5x the profit (or 5x the loss). IB charge very competitive interest rates on this $4000 loan. Its even cheaper than many banks mortgage rates. For example, I have mortgages in Australia for property I own, I pay 6% interest rates in Australia, but I can get IB margin loan in AUD at 4.713%. So I max out my IB margin to repay my Australian mortgage. Its all in AUD so no FX gain/loss to consider at all and a very simple cost saving.
Even transferring money in to IB from HKD bank account, transferring out to overseas bank account, no fees at all from both sides and great FX rates. This is why when someone ask on geoexpat whats the best way to send money overseas, so many replies will be IB even though this is not the main purposes of IB.