I owned a Speed Astir II for many years. N162SS
You actually control cruising airspeed with the flaps.
You trim the plane to fly at 55 knots at 0 flaps.
Then to go fast, dial in negative flaps.
To go slow, dial in positive flaps.

Be warned, if the ship does not have dimple tape or zig-zag strips on the wings it can have a very sharp stall when thermalling at slow airspeeds.

Other than that it was a sweetheart.