The following link from Freehills is good reading regarding on-market takeover bids. It suggests that if one decides to sell stock into an on-market takeover bid they are unable to receive a higher price later (should it arise).
http://www.herbertsmithfreehills.com/insights/legal-briefings/resurgence-in-on-market-takeover-bids
The Government provides more detail here (and this is in line with Freehills):
http://www.takeovers.gov.au/content/DisplayDoc.aspx?doc=panel_process/summary_of_takeover_provisions_in_australia.htm
