Except, I see how the airport is great if you want to board a 320/737 to DUS/FRA/MUC/CGN. But I sometimes use TXL as TATL gateway and (though I keep doing it for financial reasons) it's rather terrible for that: gate security has inadequate capacity for larger planes, lounges are landside, etc. There's a reason that the design was implemented only twice, and that the other airport that did so (CGN) reversed it.