Why the *%#@ are these on the box? Because they don't add any liquidity. ADFN is somehow associated with inca, CINN with island, and who knows what AMEX does but what's the point of redundant quoting?
The AMEX quotes are annoying and totally useless. If ISLD, INCA and a couple of other ecn's formed their own exchange, they would quickly take over trading of a handful of daytrader stocks, just like ISLD did in QQQ.
It took ISLD several years for the corrupt, bass-ackwards SEC to give them exchange status, and even then they had to merge with cinncinati...and QQQ is listed on AMEX so when AMEX got fed up with fair markets taking away their share of the QQQ volume, they whined to daddy (the SEC) who limited ISLD's ability to display QQQ data... I truly hate the SEC...the fact that they get $$$ every time I make a trade is the one thing I really, really hate about being a trader.
It's for the extra liquidity. They handle pools of liquidity for 10 or more from large institutions. When you want to get some size it there....sometimes.