First you have to be within 335 days of your disembarkation date to view and book flights.
I have used them often and I find the international flights are always exactly the same as I can buy or often much, much less. For domestic flights they usually are precisely what the airlines offer. I have never seen a situation where they were more than booking direct.
They are a consolidator just like many entities and their inventory changes daily. If you don’t see a good price check back. You can change the flight as often as you like without fee until your final payment date. I always use them as a placeholder until I make a final decision
Their flights to Amsterdam can be an incredible deal. I alway try to route through AMS so I can capture their deals - my last trip was $900 one way, nonstop business class back to DFW
PS I see you are in Australia so YMMV. Additionally when you book internationally can make a huge difference in price. I don’t know when you bought the other fare and date of booking may account for the price difference you are seeing