The small red tab is an aerodynamic balance, used the reduce the control loads required from the pilot when power assistance is not available.
Normally, the aerodynamic load on a deflected aileron will tend to return it to a neutral position. For slow and light aircraft the pilot can easily handle the required load to maintain the required deflection. For high performance aircraft these loads can be come significant.
By adding a small part of the aileron ahed of the pivot (a horn), the aerodynamic load on that portion will tend to deflect the aileron further into the flow. The tab is still small enough that the main part of the aileron will return the surface to neutral, but the force from the horn effectively lightens the load that the pilot needs to handle.
The EA300 is a high performance aerobatic aircraft. The pilot needs light control loads in order to perform the extreme maneuvres the aircraft is capable of. Using aerodynamic balances achieves that without the need for a heavy hydraulic system.
You may also find aerodynamic balances on the elevators and rudder of some aircraft, for the same reason.
The geometric shape trailing from the wing is a sighting aid to help the pilot judge the aircraft attitude with respect to the horizon - nothing to do with the ailerons at all.