Limited areas appear to be eastern metro postcodes.
Plus $10 off first order (newsletter subscription) and potential 4.2% Cashreward (may not qualify if using signup code).
Sold and shipped by Duke Living. Not as good as a previous $349 + delivery deal, but this time includes free shipping.
This one appears to be the budget "Weight Balance" model (lack of recline tension adjustment dial, hence "auto" balanced): https://ergohuman.com.au/ioob-weight-balance-by-ergohuman/
There is another "High Back" version with aluminium base: https://ergohuman.com.au/ioo-high-back-ergonomic-chair/, the armrests and seat mechanism look completely different, so it is not just the aluminium base. It is also on sale at MyDeal, but not as attractively priced, and shipping is not free.
Link to all variants: https://www.mydeal.com.au/brands/ergohuman
2022-01-14 Update: try this $10 code "JESS10" if you don't want to subscribe to newsletter. Thanks websalad for this info.
2022-01-14 Update 2: if you are not sure about this one and want to check out other alternatives online, pay attention to the seat adjustment mechanism. A run of the mill task chair would have a tension adjustment knob at the bottom (centre) and a lever on the side for high adjustment, sometimes the lever also doubles up as tilt lock. This kind of design has been around for like forever and there's nothing ergonomic about it. Manufacturers may make them in fancy shapes, or wrap them in fancy looking mesh/fabric, and give them fancy names, beware.
2022-01-15 Update: if the numbers are correct, 700 units were sold up until 13/Jan, then increased to 800 units on 14/Jan, then 900 units this morning. As of 8:30am, 11 units left, lets see if they get cleared out today. Meanwhile I'm still umming and ahing, undecided. :D
2022-01-15 Update 2: this particular chair has since been removed from Ergohuman AU website (page not found). Possibly discontinued, hence the price drop, and likely last chance to purchase. Cached product page is still available from Google.
2022-01-15 Update 3: out of stock at around 12pm.
2022-01-20 Update: chair was delivery earlier today by Border Express to Sydney metro. Took 15 minutes to assemble, if you have access to 4mm (for headrest) and 5mm (for armrests and back) hex bits and a ratchet they can really speed things up.
The chair comes with a 4mm hex tool to secure the headrest, I didn't try it but I can imagine it would be difficult to use due to limited clearance. So, if you don't have access to hex bits and ratchet, get a 4mm allen key ready. All bolts have blue thread lockers, so they become pretty tight and can be difficult to secure all the way.
Overall quality is quite good and comfortable, back is a little bit wobbly due to height adjustment mechanism, but not a cause of concern.
Didn't used the included castors, transferred the fixed feet from the old chair. Don't like chair rolling around, and also for floor protection. They are around $22 from Amazon: https://www.amazon.com.au/dp/B097YTCCZV/