I used to have a 6L (I think), so that we could cook a joint, or whole chicken. However we never actually used it for that in the end. For me a chicken or joint is better roasted in the traditional way... However we did regularly feed five, and there was always a couple of portions spare for lunch the next day (guess you would easily feed 6 adults). We generally did stews or currys, and cooked the potato / pasta separately
I now have a 1.5L cooker which is great, I use it most days, just chuck something in before work. Even just put sausages, beans and potatoes in last week... yummmm the ultimate comfort food ready and waiting for you That feeds two quite happily.