We started using it a few months back and saw a big improvement in our organic hits. You need to upload a new product list every month though as they expire. We let ours expire by mistake and when we uploaded a new one the results were never the same.
Still, seems to help us quite a bit when people search for specific items we stock.
It has done well for us for getting above the No.1 spot (in prod search results) on G for specific product searches, something which would have been hard to get against the many price comparison sites.
Not seen huge traffic yet, but there is plenty you can do to optimise your feed. It is not too hard to get to the top of these results quickly, much like the good (or bad) old days of search engines
Works well for us, need to watch out for html in your description for example <br> or <br/> is ignored so words can run into themselves if you don't leave a space before <br>...err, hope that makes sence.
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