Ann: Induced Polarisation Survey Commenced at Grace Project, page-15

Pretty sure you can't ask commsec specifically to buy cxt for you. You'll get them at the midpoint if they are there, but if they're not you'll pay market price. With cmc you can phone in and specifically order a midpoint purchase, and if there are none there you don't have to buy anything. Commsec is place your order and get what you get. Big difference. Cmc does have plenty of downsides though, but can be worth it if you just open an account and pay the monthly fee so you've got access to the occasional guaranteed CXT as long as you've got funds in the account- but that's another story and a PITA with cmc.