For anyone playing along at home, I ended up purchasing an "Easy Capper" machine, made in Italy and imported into Australia by Constante Imports. (http://www.costanteimports.com.au/wi...sy-capper.html
We've used it for three bottling runs, all up about 1200 bottles and it seems to work just fine. Easy to operate and a bit quicker than hand applying Novatwists.
I'm not sure if its user error or the fact its on a slightly wobbly table but I think around one in 30 caps go a little awry when screwing on. But it's easy to tell when it's not right, snip off the stelvin and re-do it with no harm done.