As a commercial Tiger Moth Pilot, I can tell you that the slats are a real pain. The cables used to operate them stretch over time, especially if one is doing a lot of aeros allowing the slats to 'float'. This stresses both the slat mechanism and the wing, leading to all manner of maintenance headaches. We remove the slats as a matter of routine whenever we are having wings rebuilt.
They make practically no difference to the approach/landing in a Tiger, do prevent a wing break at the stall, which is very benign anyway. But otherwise serve no useful purpose.
My understanding is that they were an extra charge option on the civilian aircraft, but were specified as standard on the RAF ones?
regards
866