Bike upgrades Redshift aero kit vs power meter

So as title suggests I am debating which upgrade to get first. I have a cube attain pro as my current road bike which I used for olympics and sprints last year.

I saw many aero bar kits but after finding redshift it’s a clear winner for versatility. The kit is about 450€ and I’ll be working with a bike fitter regardless of whether I opt for a power meter pedal set or the aero kit.

Question is which is more important, the power meter for better training over the coming months for a 70.3 in mid September or a better aero position?

Ofc the aero bars would be better closer to the day but with no measurement of power intervals are purely perceived effort/heart rate zones and so my training can’t be as regimented and how I feel one day can vary.