I've never had one until I figured out I had GPS capability on my phone
. I just downloaded a simple waypoint app (free), and it tells me which direction the waypoint is and how far away. I don't use it often, but it helps if the woods have grown up and become unfamiliar since the last time I visited an area. Also does good at recording white perch beds on open water on the lakes.
I don't have any advice, but I am interested in hearing what makes one GPS unit better than another. I don't know much about them.
Jason