I'm trying to decide if I need to find someone to review the code for the application a 3rd party agency is building.<p>If the 3rd party is going to help with iterations of the product, do I still need someone to review the code?
Depends on many things. For example: how much do you trust the company, what other products have they built, are they building a prototype or MVP, are they building software that needs to be highly reliable, secure or precise, do they do internal code reviews, do you want them to optimise for time of delivery or correctness or what exactly, etc. In any case , I’d recommend to get someone you trust to do a cursory code review after the first month just to see if they spot major red flags. Although if their code quality is bad, you’ll probably spot red flags in their product as well.