Great product with a few caveats
I sat on the fence between Bonzai and Sketchup Pro for quite a while. After using Sketchup (free) for many years, I was on the hunt for something more. I took a look at basically every 3D modeling program available for Mac, and quickly eliminated most of them based on price and ease of use. I'm by no means a professional and was looking for software that didn't cost and arm and a leg, and that didn't take training to figure out.
In the end, and after extensively using demos and beta versions, I chose Bonzai, and with a few exceptions I'm happy with the decision. Here's why:
Bonzai is fast, capable, and dare I say it, fun. To get the inevitable comparison with Sketchup over with - there is none. Bonzai has more muscle. When Sketchup's bag of tricks is exhausted, Bonzai is just getting warmed up. The fact that Bonzai is a solids modeler puts it firmly in a different class.
At first the Bonzai interface seems awkward - most tools have additional modifier settings that affect the behavior of the tool. However, after making it along the learning curve, the way they've designed the interface makes sense, and allows faster modeling. For rectilinear modeling (e.g. millwork), you can model basically as fast as you can think about what you're modeling.
In a more general sense Bonzai takes an approach to modeling which I find "neat". Not very objective I know, but suffice to say that I find modeling in it more pleasant than other programs I tried. Also, everything you do has dynamic feedback on the screen. This makes Bonzai way easier to use than some other programs. For example, I own another modeling/CAD program which, in theory, can do everything Bonzai can do and more, but I find it so frustrating than I've basically given up.
Bonzai also seems to have enough depth to it that I can't see myself outgrowing it for a long time.
Now the down sides: If you want to produce more than neat looking pictures, you will need a CAD program to export to. Although Bonzai does have dimensioning tools, the ability to easily produce drawings (for building or manufacture or whatever) is not there. This is one point where Sketchup Pro is definitely superior. On the other hand, Bonzai can export ACIS parametric solids, which I find much better than a bunch of faces when it comes to the CAD end of things. Additionally, the options for renderers available for Bonzai are far more limited than for other programs with larger user bases, (Rhino, Sketchup, etc) and consists of RenderZone, and Maxwell. It would be nice to see something in between in terms of cost and quality. Also, I would love to see Bonzai able to generate bills of materials. Presently this is only available in it's big brother Form Z, at three times the price. My final complaint is stability. Quite simply, it crashes more than it should - not the worst I've ever seen, but enough to be plenty annoying should you forget to save.