I went to a GameStop earlier today and they had it (last one in stock). I picked it up and I love it.
I was concerned that the Wii-Mote might get in the way, mounted underneath the "Classic Controller Grip", but it really not an issue. Having the Wii-Mote sitting off to the side, tethered to the Classic Controller has always irked me. Nyko's product takes care of two issues. First, it makes the Classic Controller much more comfortable to hold. I never found the Classic Controller to be very ergonomic. Sure it gets the job done, but I've always dreaded seeing the "Classic Controller is required to play this game" message. Yes, I know I could have just used a WaveBird - but...
Anyways, the second issue taken care is the most obvious - the Wii-Mote. The clip (which can be used with or without the "grip") attaches to the back of the Classic Controller. The cord wraps around the clip and just enough room is provided to allow for there to be enough slack so it's not pulled too tightly on either, while leaving about 2.5 inches at the end to connect to the Wii-Mote. The clip acts as a holster for the Wii-Mote which simply slides-in (via the grooves on the sides of the Wii-Mote) for a surprisingly natural fit.
The Wii-Mote can be removed easily whenever needed, leaving the Classic Controller inside the grip, with the wrapped-cord in place for future use. Definitely worth the $15, at least it is to me.
Also - I don't know why, but in the pictures of this product (Nyko's website, GameStop, etc.) - they have the cord wrapped around the clip wrong. It's actually a much better and tidier fit than what is depicted in the promotional pictures. You would think that Nyko would know how to use their own product (being as though the correct way to set it up is illustrated on the back of the package).