Phill,
Expect slower executions and never at the "best" price available. You can expect your fill confirmations to take forever - you have to wonder for a few minutes if you even got your fill or not.
You can expect their first phone support level to be unable to answer why a fill happened in such a manner and then you can expect a totally absurd answer from their second level specialists as to why it happened the way it did - and it will never be addressed to your satisfaction (better price).
I don't trade every day, so I can live with it. If pennies and timing is critical, move your account. You won't be happy with Ameritrade.
Good luck,
Rocky
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