The guide is certainly useful but not mandatory except in the summit areas of the volcano. The Sicilian parks as well as the Etna park are open to everyone and can be reached by car as far as the asphalted roads lead and to the equipped ski areas.
Those who choose a naturalistic and volcanological guide want to delve into the most unexplored, beautiful and suggestive areas. An expert guide will allow you to visit places that you will not be able to explore on your own and without knowledge of the area. The guide has the task of leading you safely and transferring all the information that an independent visit cannot grasp.