Ah, a complex question! First, no, not all windows are the same. Even if the specifications for SHGC and U-Factor are identical (so the theoretical energy efficiency is the same) the quality of the vinyl or hardware can dramatically result in a difference in the useful life of a window. And while thin single strength glass can have the same energy specifications, it breaks easier than double strength glass which is the minimum thickness used by Custom Windows. So be sure to compare equal quality because sometimes ‘cheap’ becomes far more expensive in the long run!
Also, remember that big-name brands also have big-expense advertising, not to mention distribution costs that increase as the cost of fuel increases. Custom Windows tries to ensure that every dollar that you invest in our windows goes to higher quality products, not expensive advertising or fancy showrooms. In fact, the only thing that could be considered an advertising expense is our web site!