to easily jack one side of the car off the ground to work on?? I would think it would be ok if you have the torque box plates as well. I like being able to jack up one side on my older cars. With the Sportlines I need to drive up on a 2x4 to jack up the front, and the gas tank hangs down too low to jack up the whole rear.
yes they can but you will most likely damage the coating on them. I just undercoated mine so it scrapes through.
the reality if you have a proper subframe it should be strong enought to hold the wieght. that being said there are alot of crappy subframes on the market. proably more than 50% are not really good enough.
If you have ever actually seen the MM subframes in person you would not worry about using it as a jacking point. the picture on the website is kind of decieving to just how rubust they are.