I never owned Mecsoft's products, but I did spend significant amounts of time doing the demos in version 5 and 6. So I'm not super qualified to make a comparison, but I did get enough exposure to form an opinion.
I found that the Mecsoft products worked well enough, especially Visual Mill. RhinoCAM on the other hand would lock up and crash a lot. I also found that RhinoCAM was too intrusive. Using RhinoCAM meant that I gave up valuable graphical real estate for the MOP pane (I'm going by memory here, but I think that's what it was called). madCAM on the other hand is no more intrusive then a toolbar, and seems to be better integrated in Rhino. In other words, RhinoCAM felt like it was riding on top of Rhino, while madCAM felt like it was part of Rhino.
That's my opinion, for whatever that's worth,
Dan
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)