just like overnet, it will use up more overhead bandwidth, but if you need more sources for rare files it MIGHT help. but until all the regular ed2k servers go down, i wouldn't use it.
You can connect to both and I suggest you do that. I often get sources faster with Kad, and a big pro of searching Kad is that it doesn't display incomplete results.
The overhead is a drawback, but I don't have a lot of trouble with that.