I don't know..i just know there is no way i'd use one. Banned in Canada for a start!
http://news.bbc.co.uk/1/hi/health/2054550.stm
To be honest any plastic contraption that stops you from holding and interacting with your baby isn't that great for it! Car seats for example can be really harmful if overused ..in other words car seats are for cars!
These travel system drive me bonkers. Babies are slightly oxygen deprived when hunched up in car seats and it affects their spinal development! Yet retailers forget to warn parents about it. So many parents don't know and keep babies in them all day I've noticed.
Best way to keep baby occupied while you do your housework and all that is strap em on your back, helps strengthen their muscles, better attachement to you, they cry less (studies have proven this) and they learn by watching you do your thing! There are some brilliant slings out there that make it very easy.
http://www.bigmamaslings.co.uk/