Every complex model is made from a lot od smaller parts.

Zbrush is superb for quick sketch what you have in head, like taking a simple pen and drawing a concept. Then it depends what you need. If game model or clean model for render, you need to retopo it.

If it is just for static render or design, you can go with decimated geo from Zbrush and polypaint it or use some box uv mapping and then paint it in some other program.

Zb is little bit hard to get at the beginning, MoI is super fast to learn, have very simple ui and powerfull tools.

Similar to Zbrush is Mudbox or 3dcoat - they have more 3d program UI, but ZB have a lot more abilities and most designers use Zb. In big productions Zb is standard.

So, complex models are realy not software dependent - it's about deconstruction what you model, think about separation to smaller and smaller parts and then detailing them.
Start from big shapes and going to smallest one.

I saw people are doing product designs in both - zbrush, nurbs modelers and even polymodelers. Software is secondary, idea is most important :)


Vojtěch