Just ask specific questions and it is much easier to answer. Most people here don’t have both machines to compare the differences. I have only used my design and much larger machines I can not and am not comfortable making performance claims or actually comparing another company’s product. I tried to stay out of this post. I do feel both machines are more similar than most think. Relative to a large $200k+ machine if one cuts something in 2 hours and 20 minutes vs 2 hours does it really matter that much? All the electronics are not different enough to make a difference, and if it is you can use any board or steppers on either machine.
Ease of assembly- have a look at the build instructions and parts lists. From what I can tell I have a lot less parts, by a very large margin. All screws and nuts need tightening over time, I think that is a big factor.
I’m not sure what you are looking for in the forum activity. The information is out there, we are not doing anything vastly different over here. The biggest hurdle for most people is not the actual machine but how to mill, CAM, Bits, Endmills. Stuff that is usually software related. Every single time a build or machine question comes up I try to help and then add the information in the site somewhere. More information=less questions.
You do not have to use the 660 on the mpcnc, there are dozens of mount for any tool you want. I have put up videos milling aluminum with a dremel, the 660 is for or 5 times the power of the first spindle used for milling aluminum. More power is not always better and at some point the mass and size are detrimental.
Have a look throught the site, there really are not that many pages. Just have a look through the first three pages under the home menu, follow through the assembly page all the way through in order and that should clear up any question you have. Other questions have been answered in the short FAQ, and then there are so many videos made by mpcnc owners. I have not given away a single mpcnc ( I gave a friend one at the very beginning but he never put it together), so every video you see is legit.
If you watch other videos I suggest turning them off as soon as they say “so and so sent me this machine, here is my honest opinion” If you give a crappy review no other company will send you free tools, find people that have bought them themselves.
Again, ask specific questions and everyone in here will help. It is very difficult to answer…is it better? Example-I want to mill 2’by2′ signs out of pine mostly, should I use 1/4″ or 1/8″ end mills?