I use the app almost every time I need gas. I search Current Location—or anywhere else. Sometimes I'll check a location I plan to visit in case gas is cheaper there.
Today, just now, I paid 20¢/gallon less because I searched my current location and found Power Plus Automotive in Belmont, MA was that much less than my go-to, Watertown Gas. The stations are ~equidistant but I would have driven a little further to save the $2.80.
At least as of this writing, I have only encountered one incorrect price—the price I paid was less. (This actually happened today.)
I didn't know I could Favorite stations until I read someone else's review. (Heart upper right corner but sometimes the heart doesn't seem to appear.)
Based on reviews, I'll skip the GasBuddy card, at least until more issues are resolved. It doesn't seem consistent, often defaults to "credit" price, and issues with double billing or inability to use the card.