Nothing special. The kits are plug-n-play now. The hi/lo kits are plug-n-play also, plus one wire you have to hook up to the battery. You want a 9007 Hi/Lo kit. I'd stick with 35w since it is more than enough.
DDM was a very popular source for members on here. They're getting out of that business though and are almost completely out of stock. So if you place an order, it may come back as backordered or unavailable.
There are lots of other companies that sell them. However most rip you off. You should never pay more than $90-$100 for a hi/lo kit. There is also a member on this forum (GGLighting
) that sells them as well for very reasonable prices. You can PM him and he'll get back to you very quickly.