I will relay my experience. I used to have their free service, then during the pandemic they offered super cheap premium membership so I did that. Now I have a paid premium account that is I believe $49 per year (I think they do offer some discounts for military/students/teachers). Membership gets you email notices about deals for your chosen airports. Free accounts get slower notifications. Premium accounts have faster notices and more airport choices, and elite accounts have even more choices and include deals for higher fare classes. You can also search for deals on their website (I think access depends on your account level).
My experience is they link you directly to Google flights where their search criteria pre-populates and then you pick dates and book directly with the airline or the third party booking service (just like using Google flights on your own). I don't believe any flights are booked directly through the Going website. The deals are often a really specific set of criteria and the ones I get are usually for very basic economy (no bags, no seat reservations, etc.). So you do have to pay close attention to the details and timing. For example, yesterday I got notified about a nonstop flight to Amsterdam from my home airport (Portland, Oregon) for $465 traveling November-March - which is a great deal. This morning when I click through to Google flights, that price is gone, though using the flight grid I can see other dates with some reasonable prices (a 10 day trip in December, $669 for basic economy or $843 main cabin). Other recent emails showed super prices but the details were terrible (58 minute layover in Chicago, no thanks).
I haven't yet found a deal I can take advantage of, but I just retired so I am hoping to take advantage of my increased flexibility. For about $4 per month I figure it's an educational experience, plus if I do find a deal that will likely offset membership cost. I'll reevaluate the value when my account renewal comes up.