In your kasut, I will avoid second hand action camera. I know osmo pocket is not strictly an action cam but it wouldn't be hard to imagine it will be treated like one. you wouldn't know how the previous owner abuse them
Some more you mentioned new op2 vs used op. Op2 has bigger sensor, and brighter lens(IINM) therefore better picture quality esp low light street walk type of scene. If you can afford new op2 why not?