The first thing to know about Death Duty registers 1795-1905 for the period you are interested in, is that they have not been microfilmed. Death Duty registers are large heavy dusty black books which after 1858 are held in storage offsite from The National Archives at Kew, at their repository in Hayes. It takes The National Archives 3 days from ordering the document for the registers to be available.
It really depends on the will how useful Death Duty registers are. The registers are tax records following the beneficiaries so they can be extremely useful since they will state what relationship the beneficiary is to the deceased not something always apparent in the will. The earlier the will the more useful the Death Duty register can be, particularly where you can't rely on civil registration or censuses. For instance they often give the married names of daughters and sometimes beneficiaries death dates.
I have found less need to use the later registers where my knowledge of the beneficiaries in wills is clearer because I have more records to go on. So it really depends on how much you know about this family.
For others reading this The National Archives research leaflet on Death Duty registers can be found at
http://www.nationalarchives.gov.uk/catalogue/researchguidesindex.aspDeath Duty Records, From 1796
Death Duty Registers, How to Interpret
Regards
Valda