Merrill Lynch debuts its first-ever online brokerage window today, Merrill Edge, consisting of 500,000 investors it inherited from Bank of America out of the gate.

The brokerage giant intends to compete with Fidelity and Schwab, where, Merrill advisers tell WSJ, the more sophisticated investors experiment with “play money” independent of their financial planner.

To gain traction among both the high-net-worth and younger investors, Merrill isn’t paying financial advisers any fees for trades on Merrill Edge; only for referrals.

Money Management Executive’s take: Merrill might find Fidelity, Schwab, E*Trade, TradeKing and others more formidable competitors than they expect, because wealthy investors—especially the sophisticated ones and those who have been stung by the recession—are more interested in powerful trading engines and low costs.  And “play money” at Fido and Schwab? Merrill Lynch advisers might be very surprised to find that investors planning for retirement are very comfortable working with the two giants.