Both the Family Finder and traditional autosomal siblingship tests use your autosomal DNA and are able to detect very recent relationships such as parents, siblings, and half siblings. However, there are notable differences between them.
Traditional parentage and siblingship tests use autosomal short tandem repeats (STRs). The Family Finder testing uses single nucleotide polymorphisms (SNPs). STRs provide more resolution per marker than SNPs. However, Family Finder testing uses such a large number of SNPs that it is able to detect and calculate the degree of relationship for up to five generations of close and distant relatives. This makes Family Finder a higher resolution test than traditional autosomal tests.
Note that Family Finder is not a legal relationship test even though it offers higher resolution results.