OK mate, gotcha. There is no guarantee what you get if you go...

OK mate, gotcha. There is no guarantee what you get if you go 'at market' - but I nearly always do get a mid point trade for a liquid stock. A strange advantage for having high SOI.

Interesting too that you prefer CMC to CommSec, because my view is the opposite.
I have used WebIress on MF Global and Macquarrie Prime and think it is much better than CMC Pro, and cheaper on CommSec if you do several trades a month. But I managed only a small portfolio on CommSec so I stayed minimalist.

1. CommSec lets you cover buys on day T+2 - CMC requires cash up front. That means you have to maintain a cash buffer if you want a fast entry to an opportunity.
2. Cash transfers from ANZ a/c to CMC take hours and transfers out a day. In ComBank/Commsec the payments are direct to/from the personal trading a/c.
3. CommSec has tremendous news flow, and a chart which shows timewise when news items happened and how the price changed. I log in just to use that feature.
4. CMC is plagued with errors and delays - even today the 'Sales' feature for 88E was non operative for several hours. Frustrating.

A full analysis would take pages - just use what you are comfortable with. Not advice.