Two very different knives, both all-around functional, but with emphases in different parts of their functionality. The handle on the companion is more ergonomic, while the handle on the 510 is more traditional (despite the plastic composition). The 510 is slightly smaller & more pocket-friendly, though not as good for longer periods of use in my opinion. Both are simply too functional & too light to leave behind when leaving home or leaving your camp site or your car for a hike.