The only argument I can understand for not commissioning a building savings contract is that the general contractor is a relative. However, my neighbor got burned by that. Among other things, a gable wall then collapsed.
I would somewhat accept it if you build with an architect who is also commissioned with the construction management. But even then, there can be collusion if he works with trades that he has known for decades. In that case, you would always have to choose against the architect’s recommendations when selecting trades, and whether he stays happy throughout...