Had to replace my wife's iPhone battery. I had all my tools and replacement battery ready--except I failed to notice one crucial detail: her phone had those blasted pentalobe screws. Khaaaaaaan!!! KHAAAAAAAAAAAN!!!
After I finished yelling, I shrugged it off and ordered the necessary schtuff.
Using the very nice pro-grade pentalobe screwdriver, I triumphantly removed the stubborn screws, shook my fist at Apple, and laughed maniacally! Mwuahahahahahahahahahahaaaaa!!!
Then I proceeded with the rest of the repair, which took only 5-10 minutes. Easy.
I'd call it a good investment to go ahead and order the pro-grade pentalobe screwdriver for any potential situations where you might have to open up another iPhone. Of course, I'm a bit of a tool junkie so I would want it just to have it, anyway. I like to try to be prepared for anything.