Why cover Scrum Asset in PSM 1 preparation?

Hi, I want to know from those who are PSM 1, I have heard from someone and from this link:

http://manasbhardwaj.net/pass-professional-scrum-master-psm-certification/


I have to do the "Developer Open" as preparation for PSM 1, I know it is too much important the Scrum master Open but I want to know if I really need to practice the Developer Test because it is too much different if I compare it with Scrum Master Open test.

I just to be sure I am investing my time in the correct path to PSM 1.