The air tech is good i know some guys who have them and they work well, the GRS is a very good cooler to but make shore you get the motorsport version of it.
if you get a second hand one make shore it comes with the diverter and brackets.
i run a GP setup with a M7 scoop if i was going to change i would go air tech personally if you go for any of GRS or Airtech you will be ok it just come down to budget.
if you want an air tech contact rich at orranje he is a very helpful guy Airtec Mini Cooper S R53 Intercooler with FREE Snoot boots - Orranje - New MINI Performance & Styling Products
hoopoe this helps