I personally haven't used any ECN before. Logically speaking, your limit order must be taken up first since it is a better price, unless someone put another order inside the spread. In that case, your limit order is partially filled, with the remaining waiting to be filled given that no one put another order inside the spread.
Just to confirm the veracity of this statement: there's no slippage for limit order in ECN, regardless of order size?
Just to confirm the veracity of this statement: there's no slippage for limit order in ECN, regardless of order size?