Looking at My Post Business link, it mentions discounts but doesn't say what they are, or whether it's a permanent or intermittent thing. I clicked the 'register' link and it asked for my business name, but not my ABN, so it seems like it will just let you register.
It also seems to be a different thing all together than Click & Send (I use click and send primarily, but I have a Business 250 membership - to get that, I did have to provide an ABN when I applied, then I had to wait for approval (there are some requirements, like you have to be sending at least 250 parcels a year, or an average of 1 every business day). The My Post link doesn't mention anything about applying or waiting for approval either, so it might be worth registering to see what the pricing is.
It might be lower or infrequent discounts (hard to tell), but for comparison, B250 baiscally gives you 10% off the normal C&S pricing for domestic flat rate postage, and international parcels (standard and express only, not economy parcels), plus (domestic) extra cover is $1.00 instead of $1.50 per $100 (SOD remains the same price).
eBay is still cheaper by far for the BX boxes, so I still buy those via eBay.
