Yes that site is safe. In fact, I would recommend only buying from that site as they don't have any 'vendors' so other sites will have second hand products. They are legal in all states except Virginia and DC. In New York and California I believe there are laws against fixing items to the windshield so obviously that includes radar detectors. In this case you would have to mount it to your dash or rear view mirror etc.
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I have a V1 and it works well for radar. If you get hit with laser you are screwed either way, the detector just lets you know you are about to get pulled over.