I was using Fiasp but every 2 days would get highs (I'm talking up to 18mmol/l here with that awful "I have no insulin on board" feeling) unresponsive to boluses, it seemed like the Fiasp had suddenly lost all potency. I ended up having to change the whole set every 2 days and then it seemed to happen after a day and a half, so I gave up and started using humalog. There are quite a few reports of this if you google it (it's a t-slim specific issue apparently - I used Fiasp in my previous Medtronic pump for over a year without issue). It's probably different for everyone but something you should be aware of - I wasn't and the t-slim rep forgot to warn me, so I found out the hard way!