Saw this as an ad and seems good value. Even the pricing on Tangerine NBN seems quite good and reviews as well.
Unclear if you can directly use the code OBS20 or have to go through the above link
edit: Rates are discounted for 6 months and hence look cheaper, but cheap is cheap!
edit 2: Manual copy paste of NBN Speeds and rates . You will get $20 on top for 1st month:
NBN - 25/5 - $44.90 for 6 months, then $59.90
NBN - 50/20 - $54.90 for 6 months, then $69.90
NBN - 100/20 - $74.90 for 6 months, then $89.90
NBN - 250/25 - $94.90 for 6 months, then 109.90 (unclear if this gets $20 off as the One Big Switch ad doesn't show this although it says on all plans you get $20 off)
To the comment that says why don't you get the referral here, I wasn't aware that you could get a referral from OZB member for $25, so yes you can do that as well I suppose