Quinn is an ADC and can be a Highly mobile melee fighter in the Ult form. Here are some pros and cons:

PROS
-Can be highly mobile in Bird Form
-Can deal a lot of burst damage due to the passive
-Has a blind, good for 1v1 situations
-The W can give a substantial amount of DPS when in Bird form

Cons
-Can be very squishy
-Proper positioning is vital

When playing Quinn, you must have good positioning at all times, or you will easily get focused, and not make any plays and impacts to the game.

Here are my personal uses and thoughts of Quinn's abilities:

Blinding Assault: I usually max this first, and harass the opponent in lane. I usually use this to also deny some of the CS when they're about to last hit. In bird form, use this to blind your opponent.

Heightening senses: I only use this when I'm alone farming. Due to the long cooldown, I only use this once in a while. When in bird form, you can use this ability to hit targets like blue buff over the wall. I max this second to get the bonus DPS from the passive.

Vault: I use this usually to mark the opponent, and deal the damage from the passive. Also, I mainly use Vault in order to escape certain situations. When in bird from, I use this to chase or escape, after using Heightening Senses.

Tag Team: I mainly use this to chase down low-HP opponents. In 1v1 situations, I use Tag Team only if the opponent is low, so you can use Skystrike and finish off the opponent. DO NOT USE THIS IN MIDDLE OF TEAMFIGHTS.