OK, I'll provide some feedback simply by using my powers of observation. I see big, bright red flags telling me that anybody who buys from this company has a good chance of getting an Equinox 600 counterfeit.
It's a new site, no info about it when searched for. There are also new sites which look exactly the same called Camelss and Goatss. Sensing a pattern here? They all have the same "about us" blurb: "...We are a small apparel company striving to bring our customers the best outfit for every occasion. We wish you a happy time shopping on..."
The website was constructed by somebody whose first language is not English. "Free ship for every order"...probably Chinese.
You say well my credit card/paypal protects me against fraud? Maybe. But even in instances where it does you're going to have a hassle. Good luck getting any recourse from your card if the detector is counterfeit. And my senses are telling me what they are selling is a Chinese made fake. The Chinese are notorious for counterfeiting popular metal detectors, not to mention anything else they can fake for a dishonest dollar.
Minelab, like most detecting manufacturers, has a MAP (Minimum Advertising Price) that by contract their detectors can't be advertised for less than. Sell for whatever you want, but you can't advertise for less than the MAP. The MAP for the 600 is $649. So how are they advertising them for $506.99?
If you buy one of these I imagine it will probably superficially look like a Equinox 600, but I'm betting it won't perform like one. And there will no doubt be minor visual tells as well to identify it as a fake.
groundsweeper is right, a legitimate dealer on this forum could probably get you one for just a few dollars more than this. And it would be the genuine article.