Well to be honest I'd go for the slow cooker. I use mine a lot and you can leave it on for hours, go away and forget it, and it doesn't dry out. You can make a variety of meals with it. I bought a soup maker 2 days ago and haven't had time to try it yet, but many people on the thread say they wouldn't be without theirs, including one staunch saucepan soup maker, who had a Damascus moment and seems to be making a lot of soup now. I think it depends on which one your twin would be likely to use more? Btw how lovely to have a twin sister! Happy decision making. 