It was very, very promising, right until the moment I started doing a real design in it. I hit so many bugs and problems, that I couldn't finish the work. Debugging constraints was pretty much impossible: if something went wrong (and it almost always did), I'd have to restart from scratch.
I can compare it to SolidWorks, which I also used, where debugging constraints is also a major pain point (why don't they make this easier?), but at least it's possible. And it is buggy, too, but much less so than Cubify, which means you can actually get things done.
From my point of view (external perspective of a software engineer), 3D modelling tools suck, in general. Few support parametric modelling, which consider a must-have, and those that do are pretty poor at it (discuss after you've created a parameter-driven assembly of multiple components in SolidWorks, and then decided to change a parameter name/value or move a parameter from a component to assembly-level).