My big problem with the t:slim and Control IQ is the way it struggles with my slow insulin absorption / fast metabolism, and also the way it over compensates for post-hypo highs.
For example, I'll deliver a bolus 15 mins before a meal and my sugars will rocket pretty much as soon as I've started eating, sometimes into the 20s. So Control IQ kicks in and delivers a bolus correction to bring it down. Then the original meal-time bolus catches up and I end up going hypo.
Also, after treating a hypo, I've noticed Control IQ delivering a bolus correction to bring my sugars back down, even when they're only about 9, so I end up crashing into another hypo. Happened a few times before Christmas, where I went from about 2 up to 9, then down to 2 again. I complained to the Air Liquide rep and they said they'd help but we've not managed to catch up since I reported it. But I know of other t:slim users who've had similar issues with an over-exuberant Control IQ bolus correction.