I have only worked directly with an external consultancy company once, and the problem (the way I see it) is that the incentives are mis-aligned. A good intern

I have only worked directly with an external consultancy company once, and the problem (the way I see it) is that the incentives are mis-aligned. A good internal developer will notice that requirements are missing, or could be improved, and has the incentive to bring it up with the project manager and get it fixed. That incentive does not necessarily exist for a consultancy developer, because as you say that means their employer loses money. My conclusion: Use consultans for very well defined and testable problems that don’t require too much business-specific domain knowledge.