I've had several models with flaps and I confess that none of them have been improved by them. Usually, the handling just goes to pieces with them down.
I'd guess that larger scale (1/4 and bigger) might get benefit from flaps, but it would depend upon the type.
The Robin DR400 had terrible flaps in the full size, so I can't see a model being improved! The Cherokee's flaps are tremendous on the full size, going from lift producing magic things to dangly barn doors that act like sky anchors. A Cherokee short field landing in a strong breeze is hair-raising for passengers because of the steepness of attitude and descent angle.

For me, the purpose of using flaps was to play at scale flying. So the flaps were used as per full-size practice. Intermediate flap at the start of the cross wind leg followed by full flap on final.
Fighter style flap selection would be at the start of the downwind leg, with a further stage at the start of the constant radius final turn with final stage flap as the turn is rolled out just before touchdown. Ideally, the throttle would not be touched after the start of downwind leg, using flap along with G for speed control. 'Hard to do in the plane, let alone on the ground!