Not difficult, just time consuming. Like 4 hours or so. I'm sure a pro could do it much quicker, but you might be out $500.
You definitely need a helper to told on to the other end. The big pain I found was having to remove the door handles, unless you want to trim the stripes just short. Then you don't need to remove them.
Did they give you instructions? You need a "squeegie" and a bottle of soapy water to spray on the car and the stripes before hand.