I have been using Fiasp for a couple of years. It certainly works faster for me than NovoRapid and Humalog ... most of the time.
I find it is far more sensitive to my starting levels - if my levels are in the 4s or 5s, I have to wait until after I eat whereas if my levels are in the 8s or 9s, I have to prebolus by at least 30 minutes and if my levels are in double figures, it can seem as if I am injecting water until an hour later when my levels suddenly plummet.
Now I know this, it is great but it took some getting used to.