I see the flex as the entry level 2x4 HD with much improved functionality and a better dac for a bit more. I believe it sits pricewise midway between the 2x4 and the SHD. For many people this is exactly what they want and need.They're a lot more expensive than the Flex and Dirac is not optional.
If you want the features of a SHD (that btw is a family of 3 products with different functionalities to choose from)... well you will have to pay for it.
I find minidsp's range fair and adequate, just imagine this company wouldn't exist!
But nowhere you get top of the line features for entry level price....