It does look a little fiddly and it can be a mistake to spend too much on these devices as they are so often superseded by new technology in the fullness of time.
Also a lot more people seem to have the linksys PAP2-NA so there is rather more available on the web forums about how to set them up.
So far as fax is concerned my fax machine broke a while back but I have an 0870 number
that lets me receive a fax as an email. This seems to be one of those few cases where a legitimate extra service is being provided on an 0870 number, except of course that I should be the person paying for it and not the person who needs to send me a fax. But nobody will give you such a facility on a geographic number.