Thanks FiatLuxDave, I think you are exactly right. Prototype/design cycle time is a huge issue with fusion, fission, and many other energy technologies. No matter how good your idea may be, you have to be able to build, test, iterate, prove, and commercialize it quickly (and ideally, cheaply, but I would argue quickly is even more important). In energy, the physics make everything work better at large scale so it is easy to fall into the "build it bigger" trap.