Amateur user: altimeter. It's fun to know the elevation of places I'm at: Japan Alps, Mauna Kea, and traveling at home on Maui. I even compare my reading to the commuter aircraft's altimeter when I'm flying inter-island in Hawaii. Everything in one instrument. What a great bargain.
Pros: Easy to use, size, fun instrument to have
Cons: None
This review was written in the old system and had content requirements that are different than reviews written today.