Sure! Just be sure to let them know that the free gift is theirs to keep if they respond, regardless of the type of feedback they give. You dont want them to feel you are bribing them for positive reviews of course.
Its good to encourage this through your follow-up sequences, through your email list, too. Your first email can thank them and let them know how to reach you if they have any questions. Your second email can ask for feedback. Your third email can expound on the tip on Page 13 with an additional resource. Etc.