Again this would not be known as crow but aileron reflex I have flown a number of Ultralights with this feature, and on one it increased the cruising speed by 10mph which is a lot considering normal cruise was only 80mph. This type had a metal fabric covered wing with full span ailerons, with the flaps being dropping the ailerons as we would do with some models - flaperons.
The reflex was set one stage past flaps up.

We also experimented with another design by setting the zero position of the flaps (conventional type, inboard of ailerons) higher than the zero position of the ailerons, so they were reflexed up. It made the aircraft fly at a slightly more nose down attitude in the cruise and again an increase in cruise speed. It is all about moving the centre of pressure of the wing.