Observation Haki seems to be slightly different depending on the user, With the same basic things, but some slight differences. That's why I don't think Luffy's "Advanced CoO" will be exactly like Katakuri's. But with Usopp his was the first CoO that we actually "saw" someones "Aura". Unlike just sensing someone or somethings presence like others we've seen (Luffy sensing Caribou's during Fishman Island) Usopp's fits more with his personally and role as a sniper, seeing the aura of someone so he can hit them from a distance. Usopp just unlocked his Haki during dressrosa, and with Wano being a battle type Arc, we could see Usopp learn to control and improve his Haki by the end of it. Possibly to the point of being able to use it to see someones "true" power through their aura. Rayleigh stated, Observation Haki can be used to sense the strength of an opponent, and used it to tell 500 beasts were stronger than Luffy before his Training, but after we've not really used that function since then. Usopp being able to tell his opponents strength right from the get go does fit with his character, being able to tell right away so not to fight head on, and depending on how it's actually used( if used at all) we could get another way to measure strength (possibly a more accurate way) than Bounties. What do you think? Could being able to see someone's power through Aura be something you want? Does it fit with Usopp?