In [1], I demonstrated a small and rather elegant MIP model to solve Numbrix puzzles. Here is the comment by Austin Buchanan:

It would also be interesting to see how this compares to an MTZ-like model. And how well the two models scale to larger grids.The Miller-Tucker-Zemlin [2,3] formulation for the Traveling Salesman Problem (TSP) starts with a standard assignment problem, and then adds some sub-tour elimination constraints. From [3]: