John...have not used one but I'm sure you can listen in to forecasts and get weather faxes reasonably well WITH the addition of a backstay antenna and tuner.
I guess my question is why you would need such a device? Most cruisers that go "off the grid" and really feel they need wefax's, get real SSB's that allow for much more information/communication and help...of course at greater expense. Increasingly cuisers are using globalstar or Iridium to download weather and serve as emergency communications....or they come to the conclusion that local VHF nets and internet cafes or Wifi can get them all the weather they need. Not knocking this choice but would be interesting to know your plans that led to your interest in this unusual product.
In answer to your other question...NOAA broadcasts SSB band weather faxes from different stations on a specific timed schedule for each particular report. It is all free...you tune your radio to the frequency of the broadcast at the right time and the software de-modulates the audio signal from the SSB into digital bits and voila...a fax appears on your screen. Unless you are skilled at reading them...you may find more value in the NavTex "faxes" they also send out. You can find out all you need about the various options here at the NWS:
Note that everything that is available by We-Fax is also available by e-mail or FTP. Click on the links towards the bottom of the linked page and you'll be occupied for hours!