I accidentally edited out the last part of my post. So to make it even longer:
I'll put out a clue about HFT trading that I have observed. Whenever I make a trade on Market, either way, it is always met by probably a number of traders on the other side in reasonable size chunks - say of more than 5000 shares each, and mostly larger. Logically, I would expect my human instigated trade to be met by a hail of smaller trades, each of way less than 1000 shares and down to a single share, if the bots actually wanted to buy or sell stock to me. But that never happens to me and I'll bet it never happens to anyone else here either. This tells me that bots are actually running in something of a parallel market, slipping between genuine trades and trading with themselves at the speed of fibre optics. I'm not sure if it is still the case, but there used to be six HFT computers tied in to the ASX computers by exactly equal length fibre optic cables*. And each of these computers was owned and operated by a different trading house. If this is still approximately the case, then none of these HFT bots are even trading with each other. That's what the XT essentially means. Because if they were trading with even another bot, owned by another organisation, that would not be an XT. Each is, in essence, its own broker.
* Back in 2012, shortly after HFT bots first arrived on the Australian market, Alan Kohler described the process:
https://www.abc.net.au/news/2012-04-11/kohler-high-frequency-trade-parasites-at-heart-of-asx/3943052
I think that since 2012 HFT bots have moved beyond legalised front running to price manipulation. It is also logical to assume that bots these days are usually working on the short side against the weight of money going into Superannuation default products and Index Tracking Funds. They are very much like Shane Warne bowling to Graham Gooch. Same Ball Of The Century, every day.
(20min delay)