I'll add another data point to this. While working for Thalmic Labs (of the MYO fame) last semester, one of the best purchases decision was to buy a 3D printer. We were able to find a big, cupboard size professional 3D printer for a great price, and we bought it. It ended up being invaluable for prototyping the design of the product. The difference between the first prototype, and what the final product is going to look like is incredible. In addition to simply prototyping, it also greatly helped in demos and testing, as we essentially had a prototype that for all intents and purposes looked fully ready at every demo, which definitely helped with testing the different sensor design, and form factor designs and getting valuable feedback from it.