Security on mobile phone: use of Identity Safe pin versus password

I just started using Identity Safe on my android cell phone.  There is an option to use a PIN versus using a Password sign on.  What is the recommended best practice for security in using these options?   For example, if I set up a PIN on my cell phone for Identify Safe, should I still log out of the cell phone Identity Safe after I use it, or is the PIN security a good option and to just sign in once with the password and then use the PIN after that?  I am not familiar with mobile security and don't want to create unnecessary risk that a virus or some other hacker method could steal my PIN and then access my Identity Safe information.  Thank you.