Its cheaper than a full Y economy class QF fare which its competing against.
You get a seat in the first three rows guaranteed - QF you sit wherever.
Access to The Lounge - QF you have already paid separately for your Club membership.
It appears free f&b/foxtel is coming so it is a substantially better product - QF you get whatever comes in a box + free drink + maybe IFE if its working.
Priority check-in - QF economy you don't unless you are a frequent flyer.
Best of all you get a wider seat with potentially only one person beside you.
Oh and for all this the price is actually $39 cheaper SYD-MEL.