Chromebook security in Guest mode ?

My chromebook is approaching its "end of life".  After that, there will be no more updates.  I do use it for bill paying and banking.  Will my passwords and money be secure if I only do this banking in guest mode ?  I understand that all record is erased  as soon as I am done as a guest.  Then I can  sign in and continue after the business is taken care of.   I love my chromebook and do not want to buy another right  now