I just purchased one of these for DS (6 months) and we love it! He has been sleeping in his Ergo Cocoon since he was 6 weeks old and loves having his arms wrapped up but still able to move them. As its getting colder I was looking for something warmer but still with the option for him to have his arms in. We tried the Grobags but unfortunately he didn't respond to them as he didn't like having his arms out.
Another hubber recommended one of these and it's perfect!
It's like the cocoon up top with the arm poppers and is 1.0 tog, but from the bottom of the chest down its like a sleeping bag and is 2.5tog so perfect for a Brisbane winter.