2003 525 bluetooth module add on

Does anyone have any experience with this product? According to bmw website it works with a whole host of phones from various US cellular carriers, but
the salesman at the bmw center says he's heard it doesn't work all that well.
There are circumstances which might cost the center an extra day or two to get it installed so I am trying to find out if this statement from the salesman is based on fact or an easy out.
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