Do you mind giving some context to this statement? What I know of the ECNs you mentioned is from reading the book 'Dark Pools'. It would be great to get some insight into the innovations that were developed in all three projects, that have become a mainstay in 'fintech'.
ECNs were f!cking amazing and when Datek started routing limit orders to Island (genius play) from retail investors the days of crazy spreads, slippage and free money became history. Some of them also allowed you to do cross-exchange routing - I think BRUT was first to do it - so you could send your order via BRUT to a specific exchange. This killed NYSE/PHL/AMEX arbitrage (AMEX and PHL were slower than NYSE so it was possible to do a trade on NYSE and take offsetting position on PHL/AMEX immediately locking the spread)
Since ECNs would self-cross at the NBB and NBA even if the market had no action because the likes of NITE and GSCO were slowing down just to get better money on the order flow, the trading simply moved to Island and Instinet forcing regular market makers to play ball.
The effect of ECNs in trading was equivalent of introducing Ansible and Puppet management in server management. Crypto-exchanges now act the same way as the who who say "We only manage our servers using Vt100 terminals using vi"
NBB is "national best bid" and NBA is "national best ask"