You need not post the same question on two sub-forums.
To answer your question briefly (based on my EX2 ownership and limited knowledge of Mirror), EX2 has more options and advanced features geared towards prosumers while Mirror is for entry-level consumers. An example, is that EX2 has support for third party apps while Mirror doesn’t seem to have any option for 3rd party apps. Since Mirror just came out and hardly anybody owns one yet and EX2 itself is only a month-old product, you aren’t going to find many firsthand comparisons…and since they’re likely gonna be used by different types of consumers it’s unlikely you’ll get a comparison from someone who owns both. You’ll have to do that research yourself. And the best source to do that research is their product manuals, which you can find here -> http://support.wd.com/product/install.asp?level1=9
You can also use their separate website info…but yes, currently there’s no quick Compare button. My personal take (based on my hunch that they are identical hardware wise but differs only in software) is that if you are a tech-savvy person who likes to tinker with technical things and are comfy in installing 3rd party apps, for which WD doesn’t offer support, then EX2 might be for you, otherwise stick with the simplified Mirror.
For the sake of fairness, I will also mention that there are many rival products from many other vendors who may offer a better NAS experience from either the number of 3rd party apps supported, a more powerful feature set or just a better UI…and even much better performance in transferring files (because of better processors, more memory, etc.) but they come at a higher price…often more than double the cost of these devices. Only you can decide what the best fit is for yourself. Do some research by googling for reviews from established hardware and gadget sies like Tom’s hardware, Anandtech, CNET, etc.