I think it is somewhat easier to hold balsa in place rather than ply! From my post I think that you can see that I use all the other methods for "clamping" as well and I do steam and it was only as a last resort that I used screws, which aren't brass, are cheap and reusable. It's no trouble filling and sanding the holes afterwards and the whole hull is then covered with lightweight cloth and Eze-Kote before painting. You shouldn't criticise other modellers because they use different methods. We all have a lot of common ground when building but we also have our own methods and if they work, why not?
I achieve what I set out to do and will continue to use screws when necessary, I think their use is a perfectly acceptable way of holding things in place. I'm not advocating their use in all cases. The OP asked, which screws, and I answered him, unlike others who are telling him he is doing it wrong. Alternatives offered are fine they aren't the only way to skin a cat.