Like with most all charging docks and their battery packs you get mixed reviews, usualy at both ends of the spectrum, either people think they are fantastic or garbage, so I thought I would see for myself.
The first thing to say is that these work perfectly fine, they charge and last a nice amount. However after charging all day and trying them out for the first time, the battery symbol shown on your Wii screen dropped from 4 to 3 with in about 20 minutes, but rest assured that this is not the case, after about another 30 minutes of playing I checked again and it was back up to 4, I think the Wii just has trouble reading the battery life when it comes to these so most people assume that they are rubbish, but they last for hours.
As for the charger itself it is perfectly fine for the price, note these charge via USB but cannot charge whilst your Wii is in standby mode, but they will charge in anything else that is on, PC, PS3 etc... The blue light that comes on signifies that there is power to the dock and when motes are charging a red light will slowly flash, it does flash forever so you will not know when your motes are fully charged, but just use your instinct, you can't moan for under a fiver.
Also the red and blue lights make it quite a festive display for this time of year.