I also trade nab online and i reckon only half my trades can be seen.I will however say that they sometimes give me a better price.Still i can't stand the practice as i like to trade in a lit market or one market and not from pools etc.
However the greatest let down is to companies themselves who's share prices are pushed down to a level where they can't raise capital at a fair price.
I also feel that the derivatives market is also tied up in these black pools and hft.
If you want to buy a stock then buy it,and if you don't then sell it.Pretty simple stuff and harder to rig.