Honestly I have a hard time seriously recommending formZ to other designers. Yes I am very fast in creating models but find a seasoned 3DS/C4D/Sketchup/Rhino user and they could likely build the same model within a comparable time frame.
Unfortunately speed isn't the only thing that matters. 3DS and C4D might lack a level of precision that formZ inherently has, but there's a level of parametric modeling that formZ doesn't have i.e. live booleans. Couple this with NUMEROUS 3rd party plugins and rendering engines and you have a hard time trying to pry a visual artist from those programs. Blender and Modo can be tossed in this mix too.
C4D also has one of the cleanest interfaces in the business, especially considering the scale of the program. Blender and Modo both have VERY nice interfaces that are modern and sleek. 3DS is a little behind in this category but they have the backing of Autodesk so it plays well with everything else that is popular from Autodesk (Revit, Maya, Inventor...).
Sketchup is extremely basic and intuitive right out of the box, which is very attractive, but the program has the ability to grow with the user because of the extension warehouse. Don't want to manually fillet that edge? Well there's a plugin for that. It was also free for a very long time and was initially backed by Google.
Rhino, IMHO is the most comparable program to formZ but I find it a bit more flexible. The Rhino for Mac interface is super clean and the more I work with the program the more aware I've become of it's expansive tool set. However it's not inherently a solid modeler so there always seems to be an extra step or to to get what I need to the engineers in my office. It also has a LOT of 3rd party plugin/rendering engine support. Oh, and Grasshopper is awesome.
I feel like formZ is best with users who know it best. I know that if I recommend it to someone they would undoubtedly come across one of the many "quirks" of formZ and I'd have to steer them away from certain tools or actions to prevent a crash (i.e. components). Having known a number of people who work in these other programs and having worked in them myself I can see why they are so popular and why many never return back to a previous program.
The unpopularity of formZ isn't because it's a bad program. It's not. It's a very GOOD program..... BUT.... the many other 3D modelers/visuallizers that have a number of pros that outweigh the cons compared to formZ.