Is multi element wing good option for slow flight airplanes?
Excellent application inverted on the drag racer, which brings home the point perfectly.  If you have enough excess thrust, devices like these can dramaticly increase Coefficient of Lift, but at the cost if loss of lift efficiency, or lower lift to drag ratio.
In the case of the dragster, more propulsion efficiency is lost if tires break loose from the pavement, so the drag of the &quot;inverted Fowler flap&quot; is an acceptable trade-off to the downlift increasing traction.
As mentioned in comments, this is why the Fiesler Storch requires 240 HP to achieve its legendary STOL performance.
And just as flaps 10 is better for lift than flaps 30 for taking off, one might question the need for the second and third flap on a lifting wing, but heavy airliners love them when coming in to land as Fowler flaps.