I was also told about Interfolio by a professor and, wanting to make things easier on my recommendors, I paid for an account. However, almost every school I'm applying to has an additional form that each professor has to fill out. (They ask questions about your academic potential, motivation, etc.) So, at least for me, Interfolio isn't feasible. I also have one professor who did not want to use Interfolio because they required him to create an account and input his contact information.
So, you should check and see if your schools have recommendation forms that need to be sent in with the letters, or paranoid professors.