After reading much back and forth on various posts on heel blisters and fit narrower than advertised I was somewhat anxious. I put them on immediately, even before changing out of my work clothes. They fit like gloves or rather socks, firmly with no tightness, maybe maybe with the exception of the top of my right foot big toe. But that is a known issue for me, in most cases my to molds the materials of most of my running shoes. An exceptions were my Adidas Marathon Trainers, a shoe I otherwise liked very much. The right toe ended up poking a hole through the mesh with the two pairs I owned. The Inov-8 materials feels yielding yet tough, I doubt I will have an issue with this. The heel feels very nice, too, and the knobby studs do not bother at all, even on the smooth surface of my home. However, I should not make a judgment before I take a run... Maybe when we have some snow.
Update: I now used the Inov-8s on several occasions. The first time, I developed some heel blisters. I taped the second time, which worked well. I meant to tape the third time but forgot. Still some discomfort after about 8 km in rough terrain, but no blister. After that, they were fine. See other entries in my blog.