Shares in the US markets are held by a Custodian (ICBC FS) in a segregated account. DriveWealth, a FINRA regualted broker dealer manages the books and records of the securities and cash.
Settlement is T + 2 business days from when the trade is placed. Execution is on the National Best Bid and Offer system. Your account is insured for up to US $500,000 under the Securities Investor Protection Corporation (SIPC) insurance. This setup is similar to all other brokers who provide trading services into the US markets.