This is a great piece for areas that are not Signet-runned, And even in some Signet areas that are obviously in your control =P, however jobs that can equip hexerai cape might find better use there, as its always got DT-3%
Its not a big chunk of MDT, but its effective and gets the job done, that on top of a small HP/MP Boost helps as well.
Worth a pick-up for any MDT Macro, rather it be for fights like Cuelebre, or Citadel Buster / etc where you'll want a good amount of MDT armor.
Now, if you cap your MDT (Shell V + about ~25(?)% more MDT in armor) you could pick up a Lamian Mantle +1, offers MDB which acts separately from MDT to reduce damage, similar to how Defense works separately of PDT (Except MDB is useful)