Tandem does not offer discounts or upgrades at this time. I had three medtronic pumps since 1997 and I just got so fed up with them. I really like my t slim - had it about a month now I guess. I really like the touch screen and not having the scroll with the arrow keys to enter numbers and there is a home button, much like your cell phone, without having to manually back out of screens. My local Tandem reps were great! Unlike the Animus people, who were pushy and rude.
I can't answer your more technical questions. It never occurred to me that someone could hack into it.
The selling point for me was that I knew I wanted a Dexcom CGM. They are submitting for FDA approval to integrate with Dexcom. There is also SUPER exciting research being done on pumping glucagon. Google Dr. Ed Damiano. There is lots on youtube and some other blogs and sites about the work they are doing.
I do know the tslim is made out of aluminum, not plastic like the other pumps. And they will fix it if anything goes wrong.
Hope this helps.