Unfortunately, there aren’t a lot of users who have been with Tandem through that first gen and upgraded to the X2, with or without Control-IQ. Hopefully you get some more seasoned answers. They just didn’t have a lot of support from the (Medtronic indoctrinated) medical community in the early days. Also, while I’m a BIG Tandem promoter, first gen products never hit the nail on the head and they had to grow based on user feedback. Overall, if you liked the original t:slim, I think you will LOVE the X2. You should notice fewer annoyances and more intuitive interaction. If you haven’t tried it out yet, I would definitely recommend downloading the t:simulator app from either the play store or apple store so you can familiarize yourself with the changes.
I don’t know a lot about the differences between models, but I think they’re largely just in the user interface, other than the obvious Dexcom integration and subsequent automation.
I’m pretty sure the fill process will be different for you, not a lot, but enough that you should watch the training videos carefully. Like, I think the having to remove the air from the cartridges yourself step will be new to you. Also, you’ll find a lot of the words in the confirmation screens to be replaced with “” and “✓”.
The “time remaining” on your IOB will disappear. Instead it will just show you how much active insulin you should still have working in you. It’s a teeny, tiny change, but one that’s the hardest to get used to because it’s such an ingrained habit.
Also, you can no longer set a specific duration of insulin action. That’s a hard one for people to accept, but the reality is that the model previously used (by all pumps, if I’m not mistaken) didn’t really match up with how people actually use up their insulin. It was just a straight downhill line (linear decay), and people had to screw with the DIA setting to try and force the pump display to match their personal reality. What actually happens to our insulin is a lot more curvy, which is what the new model uses (logarithmic decay). That model looks a lot more like the steep downhill part of a rollercoaster. A gentle curve at the top, then a steep fall, and slowly leveling out to even at the end. Because of that long tail where it’s approaching zero, it simply doesn’t matter much what your previous DIA was. The new algorithm levels the playing field, so it’s hard set at five hours, which would really suit anyone who had like a 3-4.5 hour DIA previously. Note, that’s my personal guess/observation. You won’t find those numbers or explanation on any Tandem material. As an inherently difficult person, the set DIA is my biggest complaint. I have unusually slow insulin absorption. My DIA was set over 5 hours previously. Because of that, I consistently have have hypo incidents 4-5 hours after a large bolus. The pump starts reading zero IOB around the 4 hour mark (the time actually varies depending on the size of your bolus, it could be much sooner with a small bolus), and I personally still have a lot of insulin working at the 4 hour mark. Since I like to use the sleep mode constantly for the lower target BG, the pump will increase my basal if I’m over 120, not knowing I’m still coming down from my earlier bolus. I’m a pain in the butt, though. For most users, you just need to let go of the aggravation that you can’t control the DIA setting.
The only other thing I can really think of that might be off-putting with Control-IQ, is that you can’t set a specific target range anymore. It is hard set at 110,v which is slightly higher than a lot of us want to use. That only really matters if you’re in the habit of using the bolus wizard, though, which I seldom do. I usually quick bolus.
You could always add a little bit to your calculated bolus if you use the wizard and want a lower target.
The positives of Control-IQ FAR outweigh those previous points, though. My A1c is the best I’ve ever had (5.8, and I never had it lower than a 9 in my 30-year history. I thought my doc was going to kiss me, she was so pleased!), and my diabetic life has been sooooooo much easier to boot. I can literally just guess at what I’m eating, and Control-IQ works it’s magic in the background. Again, since I’m a pain in the butt, I have to make a mental note to eat a bedtime snack if I had a high carb dinner, to cover the insulin I know I still have on board, and I give myself a tiny additional bolus (0.05 units) to prevent Control-IQ from raising my basal. It won’t increase insulin for an hour after any bolus. And then I get to sleep through the ENTIRE NIGHT without a single alarm to wake to me!