So, used the rinse aid again. Its good but doesn't shift the water as good as demon shine but I'd still use it dependent on the price.
The tyre dressing held up well on the run down to wales, the roads were damp and then dry so the tyre was put through both extremes. We've had some strong downpours since too and it seems to have held up.
These are some pics of the cars after an hour of being dressed, good strong first impression. Sling doesn't seem to be an issue, I guess it's the same as any other dressing, if you soak the tyre they'll be sling, if you dress the tyre it'll do exactly that.