They don't slip - or not that I have ever noticed and I have put tens of thousands on various pairs of these tyres over the years. They are the go-to tyres for tourists and commuters. I use them in my expedition tourer, which is also the bike I use on long winter rides early in the morning in the cold and dark when I really, really, really do not want to have a puncture. And so far, knock on wood, I never have. No slips, no flats, just a good steady ride.
There is a tendency for road riders to affect a disdain for these tyres, with all sorts of exaggerated claims for their 'enormous' weight etc. sure, they are heavier than the so-called performance tyres, but then they were not designed for racing or high performance. I do not use them on my Pegoretti, I do use them on my tourer.
They are built for reliability, but at the same time you can cover ground with them. I could not count how many century days I have ridden on these tyres while touring, or how many 30, 40, or 50 mile rides on cold dark winter mornings.