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I would not do too many of these, but I agree with Gary. As long as there are no penalties associated with the domains, owning them and 301-ing them to your website should be fine and may get some domain traffic when someone types theexactproductyousell.com Having said that, I don't think this will do what you want. If these domains don't have links pointing to them or any authority, so It's not likely to do much for positive rankings.