My IPhone 5 was about a week old when I dropped and cracked it - screen did work but the danger of glass splinters in my fingertips while checking the weather forecast, and a long life expectancy of this marvelous phone, made me move to try to replace the screen. Internet said it was simple to do, and with somewhat crafty fingers and interest for fixing broken stuff, I went ahead and collected the pieces I needed. Screen from Hong Kong, supplied with tools that did not fit. So I got the needed tools from iFixit - iPhone 5-point pentalobe screwdriver, suction cup and a Phillips #00 screwdriver that was to big - all delivered on time and to the right price!
I went ahead, instruction video in one hand, broken iPhone in the other. The suction cup did not work on a cracked screen, rather obviously, as air seeped in through the cracks in the broken screen. So this advice, generally provided in all instruction videos, is a bum advice. You can skip the suction cup. And of course, everything is a little bit more fiddly than it seems in the video. The real difficult part was the camera, sensor, and home button part of the operation. With patience, slow pace and step by step approach, I got through it, and I now enjoy fantastic phone at full splendor again.
Skip the sucction cup. Take good time. Keep very good order of all the microscopic screws - make your own screwchart if you dont have one. And - you can do it if you have some patience, and ability for fiddly work! Good luck!