I haven't got the kit, but I have the Projector 100A. When I got mine it was cheaper to buy the bits separately (trade price and free cable made the difference) and it works a treat. In saying that it's not really any different to other battery isolators in that it works, it's easy to install and it's never cause me any dramas.
Ebay used to be the cheapest non trade priced place to get these things from but it's been nearly 3 years since I got mine so prices may have changed, but I do remember there being a few reliable aussie suppliers on ebay selling them at near to the trade price I got.
One thing it's worth being aware of is the maximum 5.5m between the main battery and the isolator which is slightly less than Redarc at 6m I believe. The 5.5m is cable length not direct line so if you are planning to put the isolator in the tub make sure you run the feed from the main battery as direct as possible. Alternatively making a mount which attachs the isolator to the main battery mounting plate is probably your best bet in a D40 because there isn't that much room under the bonnet for such an item.
Cable length from the isolator to the second battery is governed by cable diameter and therefore not an issue with the cable provided in the box listed above.