I'll be honest, Sona Mid isn't a ranked comp style and if anything is more just for fun above all else. If you do use it in ranked, use it at your own risk since most meta champs right now easily punish this pick.

Honestly though this is just a super fun build that's different and most people don't expect Sonas poke power or damage to scale or really do much in the entire game so it's always fun to see reactions.

-Good Poke Power: Sona has some decent poke with her Q, and because of the fact it targets champions before minions it makes it even better with how wide the range is. Not to mention her empowered auto from her Q is just overall nuts in the longrun.

-Surprisingly Good Scaling: This pick, despite seeming like it would be bad, actually scales hella well. Your Q and empowered Q auto ESPECIALLY do more damage. Squishy targets nearly get one shot once you have Your mythic and Lich

-Useful For Teams Fights: Besides your ult and damage you gain, your healing doesn't do too bad in the longrun so you can still constantly heal while also providing damage for your team. You actually have seriously impressive power in the longrun with being a supportive damage dealer.

-Weak Early Game: Her poke power might be good but her early game damage is just overall terrible. You're not gonna get a kill right away till you have some AP items and maybe a bit of help so just be weary of any fights you take

-Team Reliant: Once lane is over, you really need your team around to make an impact. You can't solo 1v1 anyone unless you're seriously good at kiting and the enemy keeps chasing, but for the most part you need their help to keep up with the fights.

-Heavy Mana Consumption: Sona uses alot of mana, even with seraphs embrace you lose mana fast using your abilities to combo what you need in a moments notice so take caution when you go into a fight, it can easily screw you if you're too low on mana to do much.

-Useless if behind: If you get camped, killed or too far behind to make any real impact against the enemy team, you'll notice just how fast this build can fall off. You won't be able to do anything until you can keep up later by CSing hard, and Sona doesn't have good waveclear

-Poor Waveclear: Her CSing and wave clear is awful. Granted, her Q can target 2 opponents, her power to get CS and clear waves isn't the best usually resulting in missing CS unless you're really good at landing your autos or abiliies at perfect times if your Q even agrees to hit the minion you need it to.

You're pretty much all game going to do a safer playstle relying on your team to help you in a good portion of the stages. In the later game you can definitely scare the enemy with how powerful your Q+Empowered Q auto is but for the most part you need your teams help to make this damage work.

Your best combo for poke is to use Auto-Q-Empowered Q Auto for poke damage if possible. Sona actually doesn't have the best AP ratio on her abilities but it still scales decently well if you're careful enough. Just make sure when you play, you play around your team and during lane phase, do your best to poke. You do alot of damage once you manage to get your boots and first 2 items and people underestimate how much you can do.

Minus being a damage dealer needing to focus on damage, the playstyle for Sona doesn't change in midlane. You can still be a supportive champion for your team while also doing a ton of damage off your Q.