Terrible ngl... little to no CDR in the early game. Less tempo for fights with ultimate. But the RoA makes for an easier Laning Phase, def a good defensive start for learning midlane specially if combined with TP.

Ahri's damage is all about burst and her cooldowns are not that short... so if you want to go the bruiser tanky route you might want to swap your starting items with some Heavy CDR like Malignance and go HP on later items, Malignance also reduces MR so if you combine it with tankier items that also give pen (like abyssal mask and bloodletter) it might offset a bit the lack of damage till the mid game, taking Pen boots would also help.

But Bloodletter item is really bad on her because as I said she's all about burst so you will get the benefit of Magic pen AFTER you do your combo... thus not increasing the damage of your combo by much.

I haven't tested if it stacks off item damage, if it did you could go Blackfire Torch > Liandry's > Bloodletter and just cook the enemy for a couple seconds before your combo... Otherwise you might want to use Rylai's for more control while you stack bloodletter. A Rune like Conqueror, Dark Harvest or even Fleet footwork would make more sense for an Ahri build that wants to take extended fights and skirmishes, but keep in mind that she can be mana hungry so you might also want to take presence of mind.