The first page of the article points out that no single hard drive can be a truly secure backup medium for the same reason you have to have backups in the first place: the high rate of hard drive failure. The overall conclusion of the authors is that the products they review are viable short-to-medium-term solutions for small and medium businesses.
As for the products themselves, they range from the Accordance ARAID M100 (a mini-RAID system using two notebook drives) to the 7-bay High-Rely in its 19″ rackmount (kids, don’t try this at home), the Iomega REV external SCSI drive, and the StorCase Data Express (an internal USB 2 drive). Each product has its own strengths and weaknesses, of course. Read the article and decide for yourself whether one of these is for you.