I also just stumbled across them. A quick search says they've been around for 2 years and are likely safe. That said, I have no experience with them, but they do have 2 active coupon codes.
save10 - $10 off
save5 - 5% off
Well, I'm trying them out, so I should be able to report back in a week or so if there were any issues. Ordered an EG4 battery, they said they work through Signature Solar, so it'll ship from them. They also only charge tax to orders going to Colorado or Florida, so there's a savings there if you don't live in either of those states.