Can you explain what the advantage of the gene drive system is here? Looking at the paper, I see "Cassette exchange progeny" was only successful 0.05-0.38% of t

Can you explain what the advantage of the gene drive system is here? Looking at the paper, I see "Cassette exchange progeny" was only successful 0.05-0.38% of the time (table 1). So they need ~10,000 flies to get 10 mutants. Then in Supp Figure 3 I see detection of the "modified" DNA in the WT flies, and Figure 1c shows a good proportion of WT flies (denoted as "+/+" in that figure) were infertile as well! So it seems if we just select those pre-existing infertile mutants we can get the same effect as using all these gene modification and gene drive techniques. I don't see what the advantage is supposed to be.