While I can't comment much on the Mellenium M-150, I will say I own the Mellenium tree seat. In my opinion it has no rival! Built well, very comfortable, quick set up and carries great.
However, my tree stand experience is with climbing stands. I have owned most of the popular models. The Sumitt Goliath is the best I have found. Once you get settled in with your HARNESS on it is as comfortable as sitting on your sofa. As for sleeping....someone mentioned earlier it's never a good idea to sleep in any elevated platform. But, I have dozed on many occasions in the Summitt climber and it's nearly impossible to fall out. I've harvested about 40 whitetail with my bow, all but two were from tree stands. Love watching the woods come to life sitting in my tree stand.