Air mass meter

[sebin90]

Hi there!
I have little problem with my air meter (I think this is it). I got readings in ISTA lower at about 15% than expected. Engine is N57 bi-turbo 313HP.

As result I am getting hardly 260HP instead of 313HP. On another air mass sensor I got 280HP.

Tried cleaning but no result.

I want to buy new air mass sensor, but there are brands as Pierburg, Hella or Hitachi avaliable. What should I buy? OEM from BMW is 3x more expensive than Pierburg which is most expensive one, I need some advice