It is physically impossible to use the plastic card as shown, unless the battery has already been loosened by some other method. Is the photo provided to justify the use of an extra tool?
What is unfortunately unclear is just how to 1. apply sufficient force and keeping the phone secure with only one hand, 2. whether this is best done on a table to use its opposing surface to secure the phone.
The suction cup is a worthless tool because flexes too much to provide a good hold. Mine slipped and popped away three times. -The last time causing a crack in the screen.