Short answer: yes, Pro Plan is one of the good ones and yes, it is very akin to McDonalds. For all of you who doubt this, McDonald's employs nutritionists in the same way that Purina does. But that is the way of commercial animal feed, or food in general, so no surprise there; it's a business. The person was right, but not right about this particular Purina line (you can compare Alpo and Pro Line, both owned by Purina, to really see the difference.)

The FDA regulates dog food (not the WSAVA or the AAFCO which provide frameworks to which the animal feed manufacturers comply...or not, it's up to the consumer to decide if they want to purchase animal feed that has followed the guidelines, and something to look for on the packaging), and the only FDA requirements are that the ingredients are fit for purpose and the labeling is true. There is no pre-market testing; as long as the ingredients are fit for purpose and the labeling is correct, dog food can go straight to market. (Unlike the EU FEDIAF.)

What this means to us individually is: our dogs are 100% dependent on us, so the best thing to do is read the ingredients carefully, buy, and then decide if our dogs are happy and healthy (poo, energy, coat, etc.) You can read a lot on dog nutrition, but generally it all boils down to what's in it: Highest protein with lowest fat and fillers wins. While I'm always wary and generally speak with my vets, this is a good site to start with, and Purina's Pro Plan, while not the best, is good.