The link doesn't work, but is that the Booster II attachment? I have one of these. It's not that useful outdoors, because it's kind of awkward to shield the probe from stray light under bright conditions, particularly if there is any wind. Much easier to use a regular spot meter.
In the studio, it can be handy, though, and it can save some calculation for bellows factor, filters, and such, though those calculations aren't really that difficult. In fact, I normally just plug any filter factor into the ASA setting on my meter, and I have a table taped to the back of each of my cameras for converting magnification factor into exposure factor.