I have a 4 year old and 2 year old. The Merc price for the 3 to 12 year old is £ 200, but I've only found another seat for 0-18 months, and that's £ 260. Does anyone know of any non-Merc seats that are compatible with AKSE ? My SLK is the facelift 2000 model not the current one. I saw the transponders only for sale on an auction site, but can't be sure if they're correct and my children are worth more than saving a few £s on a gamble.