A great deal and might as well go ahead and get them. We use our z vibe 2x a day so they will come in handy and there will be no delay.
Please note: to turn the unit on, twist the switch tip in *just* until it starts to vibrate. Any further will not increase the vibration, but significant over-tightening (although hard to do), may damage the motor.
Caution: contains small parts that may pose a choking hazard. Please handle with care.