Our son is 6 months and weighs 20lbs (he is our Mr. Chubby) His car sear only goes up to 22 lbs so we are in a quick search for a new one. We are going to go with either the marathon or the fisher price that is similar to the marathon, but less expense. I have read that the Britax has extra features that the fisher price doesn't..such as rear facing tether. What is a tether? is it the same as LATCH? Also, does anyone know what other features the britax has over the fisher price? I have done some research but I am not very familiar with all the car seat lingo and I thought you all might be a good resource for me and my time crunch! Thanks!