I've had my Calvers for about 150 miles (~250km) now, and both the uppers and outsoles are holding up great. The durability is refreshing after a pair of Altras essentially disintegrated within a few months.
The grip is solid in a variety of conditions, but especially in the mud. It's some of the most versatile grip I've found. However, I have had some slippage on algae-covered bridges/rocks like you might find where I primarily hike in southern Appalachia, though just about any other shoe would struggle on those surfaces. A softer rubber compound might have more grip in these areas, but I'm willing to make that sacrifice for the added durability.
I find the shoes comfortable while also providing great ground feel. For longer hikes, I did find my feet getting beat up, especially on descents littered with small, sharp rocks. Adding the OrthoLite insole was enough to fix this for me, and I assume a rock plate would be a good solution as well.
Overall, I love these shoes, and unless I need a warmer, water-resistant/proof option, they're my first choice when heading outside!