The boyfriend: Picked up two of these so we could play RE:UC together.
Pretty good, but as it has been mentioned already, you can't really sight it in properly unless your rig is set up -just- right. You would need to stand at exactly the right distance from the sensor bar, the right height, and NOT MOVE.
One thing you may not realize until you get your hands on one: The grip is far from ergonomic. Its a thick-arse brick that doesn't exactly sit comfortably in the hands of anyone without gorilla paws. Its acceptable for reasonable playtimes, but it hurts after extended play (not as much as if you tried it with just the Wiimote, however, which is the point).
Last (and definitely least), the nunchaku bypass doesn't snap into place as securely as the slot on the Wiimote. In fact, you can actually just pull it out without retracting the clips. It fits pretty snugly to stay in the slot otherwise, but if you pull, it will come out.
Overall, its still the best gun peripheral atm, and you really can't beat the price. However, the above gripes in mind, its not that much better (or better at all perhaps) value-wise than the zapper package, being that the zapper comes with a game for only $5-7 more (also, don't forget shipping, since this isn't available in stores). If you needed a second gun, though, this is definitely your best bet.