I have never heard of dumping the flap in the flare.
At low speed you would drop like a brick with the nose dropping.
I have been taught though to dump flap after all the wheels on the deck to to stop gusts getting you up again, and to give the wheels more grip. Manual lever flaps lend themselves to this but electric take a bit more time.
If you want undulating runway try Barra it changes every time the tide comes in. Landing wasn't to bad just drop it on the top of a rise. Takeoff the sand sucks you down so when you do unstick you feel as if you leap into the air.
MJ