My experience with Garrett Australia when I needed a warranty replacement was actually good. I'd bought the unit from a Tasmanian dealer who very shortly after selling it to me went broke owing Garrett thousands. They still replaced it as it was bought in good faith.
I wouldn't say the ATX is as good as other machines. I know two people who have had one and didn't like it / don't use it. But they do find gold. And if you scour the forums you'll find dozens of posts with people who bought GPZ7000s when they first came out, didn't like them, and went back to their old detector.
I think it's a common mistake to buy an ATX / GPZ / GPX 5000 for their one's first detector, when you don't know how to detect yet. If I was going back to buying my first detector, I'd buy a secondhand GP or SD series, or an SDC if I had the budget, and upgrade to a more complicated detector when I had the confidence that, if there was gold to be found, I was able to find it.
Just my 2c.
Edit: spelling.