If your goal is simply to detect duplicate samples, then dupcheck is the more efficient approach. Ibds assumes a population frequency model and is uses it to detect more distant relatives, though in a somewhat crude way. There are more specialized packages that will do a better job.
Dupcheck and ibds will both find samples that look like MZ-twins, i.e. where concordance is nearly 100% or IBS2 and IBD2 are close to 1. ibds will often find more than dupcheck, e.g. parent-offspring pairs (IBD=~0, IBD1=IBD2=~0.5), sib-pairs (IBD0=IBD2=~0.25, IBD1=~0.5), etc.
Hope this helps,
-Kevin