I've had a very negative experience with Neptune Systems. Now to be fair this was an aquacontroller system I bought on Reef Central, but it was a setup that had been purchased for a tank they never setup and never used. Everything was still in the original bubble wrap etc when it arrived.
It was supposed to have a serial port, and the Neptune Systems box was labelled showing a serial port. However it was a unit without serial port. Aquacave was the actual vendor and when the original purchaser contacted them, they acknowleded the problem and refunded the difference which was sent to me. The owner of Neptune Systems, however, was a different story. He refused to replace the improperly labeled unit even though I offered to pay the difference. In addition from the start he was hostile and defensive, refused to acknowledge any possibiliyt of a problem or error, and was outright rude.
Bottom line, Aqua Cave good vendor, Neptune Systems bad vendor.