This is a carbon copy alternative to the regular product that you'd normally have to buy. The only difference that I can see is the 'Millennium' logo on the front plate. As anyone who's worked with Sennheiser UHF gear will know, the spares and accessories, whilst excellent quality, can be quite expensive.
This kit fits the G3 units perfectly, with no hassle. The 'pairing' plate, and all the little screws and plastic plugs that come with the original version are included. I'd thoroughly recommend this kit because it works perfectly, and can save you quite a bit of money.