The instructional overlay appears every time I open the app. Fortunately it closes by tapping anywhere on the screen. I wonder why they used a bracket to call out the function of two buttons.
The 'By Price' feature is slightly confusing. At first I thought perhaps a drop-up window would appear. Rather it caused the list to change order so my first assumption was that it sorted the list from least to most expensive. That theory was upended when I noticed the label changed to 'By Distance.'
At this point I was annoyed. I couldn't determine if the label represented the list or that it indicated the list I would see if tapped. Since then I noticed the list is now titled to clear up the confusion of the toggle.
No critical usability errors here, and in the end you can scope out how much you're about to pay and how cheap gas is on the other side of town. Get your GasBuddy app here: http://www.gasbuddy.com/GasBuddyMobileApps.aspx