One thing I cannot fault BookMacster for is it's willingness to offer support. (thank you Jerry)
However I am not a happy camper.
1.  The problem of Bookmacster not being able to handle a duplicate bookmark (even when placed in a different bookmark folder) did cause a lot of problems and despite me following the instructions is still not consistently solved. (when restarting browsers on other Mac it is back to square one for no apparent reason and I can't be bothered to keep repeating the instructions) I now have a simple workaround via a different route which is to make the duplicate bookmark slightly different (i.e. for a different page on the same site)
2. I have just noticed that a separate main list of bookmarks I kept in Safari in a separate bookmark folder have all disappeared ! All that is left is empty folders inside the main folder. This was a massive directory of bookmarks I have saved and updated over many years on hundreds of useful subjects, all in separate folders E.G. Airport Parking.
The whole lot have gone.
Pete