Although my new bird has 'em, I haven't flown it yet - so I can't speak from experience.

If I remember what I read the other day, though, they increase your bird's stability.

Placed outward, (toward the paddles), offers greater stability. (The item said this was best for training.)

Move them inward for more stable aerobatics.

Use two on each side, one inner and one outer, for the greatest stability. (I've haven't seen anyone set up like this, though.)

Have fun...