Are GPS devices wirth while?

I always live in great hope that gps devices or aps will help me. I recently got an iphone and was eager to try out gps aps. Some of the ones I tried, work to some degree. I can while at home or standing still somehwere, check out what is around me. This is interesting and helpful. But, this morning, I tried using an ap while going to a familiar destination. It gave me wrong directions and told me I had reached my destination a block and a half before I really had done so. I put the phone away and just concentrated on walking with my amazingly smart and good looking guide dog and using my common sense and mobility skills. These aps are good for some things but as of yet, haven't found one that works well for me while traveling. I will say that I haven't yet tried the expensive aps and am not sure whether to or not.