Don't worry about the extender, but here maybe this will get you some sales, I installed one a while back and I love it. I've had these on my last 4-5 cars. Great mod. I thought the extender/adapter was necessary but I could be wrong. In any case I have one installed with the valve. Also free pro tip, you can get a nipple or just use a piece of hose to help point the draining oil wherever you want it to go.
EDIT the valve I have is one of two I've seen for sale, mine does not have the nipple but it still works the same way. That nipple would be helpful though I'd recommend that for sure.