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Hi Laurean, OSE is short for Open Site Explorer.

The value of links from all large directories like BOTW is debatable. We know that Google has devalued these links over the pass few years, but some webmasters feel they still pass enough value to justify the cost. One thing is for certain: they are no longer the "must have" links like they used to be. You can group DMOZ and Yahoo directory in this category as well. If it's within your budget, these links certainly don't hurt and, of course, they are fairly easy to acquire. In my personal opinion, (and this does not represent an official Moz stance) if you actively and successfully peruse other link-building opportunities, it may not be worth the expense of these types of directory links.

I looked at the directory maybe a month ago and a lot of the links were not working or were very expensive which may be why there was so many thumb downs. A cost column would be helpful