Just brought a pair of Cumulus 13 having spent the last three years running in Nike's Vomero.
I found the heel is held well and the cut of the shoe around the ankle is low so unlikely to cause any irritation there. The cut of the shoe around the midfoot is snug but not too tight, just holds the foot nicely with more room in the toebox.
When wearing them, you can really tell the gel cushioning system in the heel but also in the forefoot too so it feels like a really soft ride. It feels superior to the Vomero's cushioning, probably helped by the fit of the shoe which was better and felt more anatomically correct.
Really like this shoe, can't wait to race in it and see how it fares. It'll take something special to make me change from this shoe.