I've previously experimented with different materials for take out like stainless steel because I'm not a fan of the idea of hot food mixing with the usual plastic containers. I've found that 1) it gets way too hot and taking off the lid is torturous 2) not leak proof and 3) the shapes they come in (usually cylindrical) are impractical to eat out of, I'd have to tilt the container to get soup or food at the bottom or my put my hand deep in, scraping the oily walls of the container. Otherwise, I would have to pour the contents into a separate bowl and then need to wash two containers for my one meal.
I just tried out my kuupa today and it's truly a dream come true!! Really leak proof (tested with both just tap water and then hot spinach soup), just gotta make sure you close it all the way. It's collapsible, so I can compress it when I'm done – great for storage or just throwing it into my bag if I'm out and about. The silicon also doesn't get too hot, so I can take off the lid with ease. The bowl shape also makes it perfect for eating my food straight out of. Also bonus that it looks really cute :) I also made a mistake on my order and Chloe from customer care helped to sort it out in no time, and I received my duet just 2 days after I ordered, so A+ customer service and delivery time!
My only gripe is that they don't come in more colours. I'd love to see more colourways in the future (dark grey and/or mustard yellow would be a dream!). It'd also be great if the air vent isn't detachable (that is even when you take it off, it remains attached, e.g via a strap) so that there are less components that could go missing. :)