Hi Paul ...
I will throw in an opinion here.
MoI is the best of its kind in my opinion and I have been a user for years. I am an architectural designer and I do as much of my design and modeling as possible with MoI as it has the best workflow I know of. Yes, I have to switch to other software for some things like dimensioning and rendering but it still makes my workflow as smooth as it can get.
AND the MoI forum is also the best ever. I don't have any knowledge about how big the user base actually is but you can get almost instantaneous feedback and good answers any time day or night.
It is the best software investment I ever made.
eric