Friskies? Purina? are those useful?

My two get fed Friskies canned food and Purina One dry food (the chicken kind, the label on the front is orange unlike others that are pink and purple). They have been perfectly healthy for almost 4 years and 8 months (each cat respectively), the vet has no problems with me feeding them those brands...especially considering the closest place where the "good" food brands previously listed are stocked is over 2 hours away, and with gas at $3.50/gallon right now I'm not taking a 4 hour trip for cat food :P