I started on a pump in December. I was offered Medtronic 640 (rejected that because it was old technology) and they weren't offering the 780 at that time. Omnipod (interested as being tubeless). There was another couple, which I wasn't interested in. I was thinking of the t-slim, but although I liaised with the team and the local rep to try and get this, the team were given a training session, but not provided with one for me to see, and arranging to get one would have been another 2 or 3 months. In the end I went for the Omnipod Dash. Downside was that there were no official options for looping with it, However, as I wanted to get started I went with that one. Been very pleased with it, had some pod failures for various reasons ranging from trying to set a temp basal while I was out dog walking (it had problems communicating with the pod - ending up with a 'screamer' and no option other than th deactivate the pod - strange that it did this OK, when I was not talking to the pod!) and one that was dislodged by around 30 Kg of puppy-assistance! The other thing with the tandem was being restricted to the Dexcom sensors, which I wouldn't be able to get funding for - and self-funding would be 10% of my income!
Since April, I have been using a DIY loop (Android APS) but this does involve carefully following the step by step instructions to set up the software and build the app - and of course, there is no technical support from Insulet, only from within the online groups and forums, so it has to be approached with caution. I'm also using another 3rd-party app that reads the bluetooth signals from the Libre 2 and shows the results in real time, making it effectively a full CGM sensor, which Abbott didn't implement in their own app. That feeds the readings into the APS loop. So, it is possible, but certainly not as easy as a commercial system.