Everything is 4-off...
However, every incorrect path gave me the distinct feeling that it couldn't be right, and the solution itself wasn't very fulfilling.
Wow, luckily I was able to narrow down what I had to search, this was really only possible using careful cost-analysis on each of my many 2-offs, great challenge.
This puzzle doesn't work quite as well as your previous levels, as there are (at least) 3 solutions, and choices are limited throughout, with the few close-to-optimal paths being more complex than any of the solutions.
Great puzzle, it's quite difficult to figure out what to do and the optimizations are tricky as well, but it's all very doable and the design is well-focused.
Insights