Lady Blodwynn
I wouldn't call it a wasted purchase as the books are a veritable treasure trove of fluff and other choice bits of background information regarding the Deathwatch and their modus operandi.
I had gotten it for a singular purpose, and that was to run a Deathwatch campaign so for me it was a waste of money since I never used it for its intended purpose and I haven't really looked at them since I bought them.
I suppose I could always re-sell them but I'd never get my moneys worth back so I just keep them in their dusty decrepit corner...