I have the Terreno 2.1″ on my 29er as I basically wanted it to be as close to a gravel bike as possible.
They’re really smooth and fast on roads and good tracks, I think on a 35min gravel climb near me I was only a couple of minutes slower on the 29er than on the gravel bike (which has 38mm Terrenos).
I got carried away and tried using them on a big (dry) day out in the Cairngorms and even there they were mostly excellent except for washing out on one skinny rubbly bit of singletrack where I wasn’t paying attention.
Basically Terrenos on the gravel bike and Terrenos on the MTB are making me re-evaluate what semi-slicks can do, everything except loose steep or muddy gnar it seems…