Spot is for your loved ones to let them know to are fine.  It is reliable enough for me to not worry in the Q or BWCAW.  And I carry it in my car rest of year in case of an emergency and no cell service.  If you want higher reliability or heading north or south of the satellites Spot uses or worry about being down and unable to move under dense tree coverage or in a deep ravine or cave, get a PLB.  It has but one option and it's nuclear, but you'll be rescued anywhere in the world.  May have been on solo tripper but ther are some really good posts on this subject.  Also two reports on QJ I think of actual emergency use of Spot.  Made me feel more secure.