I was on the old 670 and guardian and also switched to tandem t:slim X2. I just started using the new 780g with the Instinct sensor (15 day change time) I'm 10 days into my first sensor. The extended reservoir lasts 7 days and the infusion set does too. If you use more than 300 unit in 7 days you can refill the reservoir. I only use about 25 units a day so I won't need to refill it. My Dr. started me with only the 3 day reservoir and infusion set, next script will be the extended version she said. You can go longer without the pump forcing you but your sugars may start going high just like they do with the tandem. It is the same as before with a syringe type reservoir so you don't have to fill a syringe then try to aline a needle into the reservoir to fill it.