While the second point in aura is good I really think you can't afford to go that skill build at level 3. Level 2 of firestorm is even more important, as is having level 3 firestorm by 5 and you need the point in pit. Two points in aura puts you all in on right-click laning for a critical portion of the game and as a very frequent offlane player I can tell you this is unreliable at best, game ruining for you at worst. Most trilanes are just too deadly, and even certain solo supports can give you a hard time, namely disruptor and the odd zoning silencer. You need to be able to bounce between your jungle and lane effectively farming up both, laning whenever it's safe. This is a huge strength of underlord, being able to jungle effectively to mana boots with just a quelling blade and one shrine usage.
Two points in aura drastically cuts your jungling speed while two points in firestorm lets you farm much faster and accelerates your mana boots, thereby accelerating your mek, and then your team's ability to fight with you. Additionally the second early point in aura ultimately delays your 4 points in pit, which is also really important.
There will be certain situations where two in aura is good, easy lanes or 1v1s against right clickers can present a good case for it, but I think any time where you aren't 100% safe in lane it is less than ideal. Often the damage output from firestorm will be your defense as well, tossing it down most people will be afraid to spend time in it, much like a march.