it works just like the naz. what i've noticed is nyse quotes are taken out before arca many times on more illiquid issues and you're sitting there waiting for a fill and then they drop it. so to say $2 per thousand could cost you much more in missed fills. but for fatter moving stocks its ok. now if you post on sdot and arca's the best bid or ask they'll reroute you and charge the .00025 fee plus your base rate. persoanlly i think it's a precursor to a total move to electronic in the next year. how the heck can they pay you a rebate on 1 side and allow you to exit sdot on the other with no fee?