Here is the BSL ABC, good luck trying to write or read reference books written with that! How does 'SIGN SOLUTIONS' expect to enable deaf who cannot write or read plain English or, the BSL version and its grammar? (Perhaps the clue is in what they do, i.e. sell a BSL interpretation service!).
Surely translating text to sign does little to enable deaf to read and write it? Why bother when SS is doing it for them? Perhaps try the USA approach? (But you may need a rosetta stone first)...