If you are getting a large tank I would be extremely hesitant to try and and go cheap on the manufacturing. I have heard of one locally that supposedly came apart at the seams, and have also heard rumors of them having it leak at a trade show. As I have not seen either I cannot verify, so don't take this as solid fact. I just know that when something comes in at half the price of the next cheapest competitor it causes me to raise an eyebrow. When looking at the total cost of a reef aquarium setup long term the cost of the tank is actually relatively low, but is by far the most important part. My concerns also arise from the plastic trim they use even on 1000 gallon+ tanks and the fact that they say you can have a tank in 4-5 weeks that is already cured and ready for use. Final personal concern is that they list their sizes height x length x depth which is odd since the engineering standard is always list length x width x height, this might be a personal pet peeve but to me it is about like trusting an editor that doesn't know the difference between there, their and they're.
I guess my point is that any red flags on a large tank scare me as that amount of saltwater can do serious damage to a house not to mention something happening to the tank will likely result in the inhabitants death. It is really up to you but this is my opinion. Could the customaquariums.com tank work just fine? Probably, but that just isn't enough for me when you are talking hundreds of gallons of a corrosive liquid containing thousands of dollars of inhabitants over thousands of dollars of equipment inside my home.
Planet Aquariums is a good option for large aquariums or custom aquariums, they don't sell direct but a substantial number of retailers use them. They are based in Plano, Texas and I would almost guarantee your LFS can get in touch with them. My understanding is the builder stayed there when Oceanic moved and that is when he started Planet. My aquariums have come from them and I assure you thee quality is top notch, he uses both starphire and optiwhite glass (as well as standard) and can do external, ghost and coast to coast (peninsula style) overflows as well. I have also seen tanks he has built with elaborate Eurobracing to avoid light blocking supports and triple layered PVC bottoms. On large aquariums I have seen of his there is stainless steel bracing in place of plastic. The local stores here all use him for custom/large builds, I have seen quite a few and all have looked quite nice.
That said Miracles and Reef Savvy are both premium tanks, structurally they do not seem anymore sound than the Planet tanks, but something about them is just much more aesthetically pleasing.
Planet is about twice the cost of the customaquariums.com and Miracles/Reef Savvy are about twice the price of the planet