I've posted about this a few times lately……
Had a pair on my new Genesis about 3 or 4 months ago. I rode them on my local trails – loose rock, wet roots, technical DH. No problems. Have ridden them at Afan, and used them for a 12hr solo at 24/12 (which was rather wet, and rooty in places). Absoluteley no problems with grip. Tidy handling, fast running tyres.
If they were useless they would have been straight off the bike as I've got a few spare pairs.
However, I was plagued with thorn punctures. I was repairing the tubes last week and had to chuck a few tubes out purely because of the number of holes in them. No thorns at all, just holes.
So, summary. If you don't expect them to have HUUUUGE amounts of grip (just look at that tread pattern!), they work well on almost anything.
For me.
Here in Wales and in Newnham.
But don't ride within 100m of anything sharp.