I don't recall the Nunchuck ever holding Motion Plus, be it Nintendo's official product or non-official ones like this... I think those two reviewers are confusing the Wireless Nunchuck in question for another accessory. The product doesn't list Motion Plus as one of it's features, so yes, I believe you've misunderstood the product in that regard.
However, since it doesn't have Motion Plus, this nunchuck should work perfectly with your Wii Remote with the built in Motion Plus. You should be able to get a refund since this nunchuck doesn't work as it should, whether it's because of bad design or you got unlucky and received a broken one. If you have any other nunchuck that work with your Wii Remote +, you should definitely be entitled to a refund.