Rear mounting carrying system. Recommended for ages 9 months to 5 years so long as they're not over the maximum weight of 22kg. The manual says can be used on bikes with wheel diameter of 26 to 28 inches. We used this for our kid and it is quick to click on and off (once familiarised using manual). it was a great way to take them along (keep them wrapped up as they don't get as warm as the person pedalling). This model has been very reliable and is still in good condition (see photos), selling as outgrown. It was not involved in any accidents and is in full working order.
eBay