Hardware startup? What surprised you about forecasting your business?

It is hard to respond to your question without knowing where in the development cycle you are. Have you got working prototype? Are you at the ready to manufacture stage? etc.

In my experience, the firmware development cycle is far slower than for native software. The interactions between electronics and the code can be very difficult to debug. Getting the power source to work reliably. Manufacturing the case in volume can hard to ramp up. Injection moulding, assembly, retail packaging, etc can cost more to develop than the product.

When you write that your unit economics are good, I wonder how far along the path of being ready to manufacture, package and distribute you have gotten. Any team experienced with manufacturing consumer electronics at scale would have prior experience with all the necessary steps. If you are looking at sub-contract design/manufacture, then you need to make a very substantial up-front investment and guarantee certain volumes, etc.

The engineering discipline in getting iterations done in hardware must be much more rigorous than in software. Get people used to designing hardware, or it comes back and bites hard.

your question is too vague, rephrase or come up with a list of clear questions?