The single twist wire snaffle is a very severe bit for two reasons.
Firstly, the thinner a mouthpiece is, the more severe it is. So, by definition this wire snaffle is very severe.
Secondly, the fact that the wire is twisted makes it strong across the bars and tongue of the horse's mouth. The slow twist snaffle, while more severe that a regular jointed snaffle, is not as severe as this twisted wire snaffle.
It goes without saying that these bits should only be used by very experienced riders, with educated hands. Although personally, I can't imagine a horse that would actually need one of these bits.