I bought some of the flux a few months back, and I am now a total convert, no more nasty fumes when soldering, is a good enough reason if any to use it.
As regards to dirty tips, I no longer use a sponge, but follow some advice given on the old RMWEB by Jazz (if I remember correctly) and that was to use a tip tinner/cleaner (got mine from maplins) and a stainless scouring pad from Asda. My tip is now like new, always shinney and ready to pick up any solder. I cannot recomend this technique enough.
J.P.