Thanks Jason - I didn't necessarily think it would be too straightforward. In this case its not a page behind a log in. Its basically just what any other site would have as a normal homepage. I did say to them that it wasn't foolproof anyway - as you say we don't have control over visitors cache or cookie history.
I asked if they had seen other examples doing this, expecting the answer to be no, but of course they had. I don't really see the point myself - I'm wondering if they've seen something about how it could have SEO benefit.