Sorry for all the questions but this is all sooo confusing!!! I'm switching my 6 month old out of her infant seat so I'm looking for the best seat for her. She is tall but only weighs 15 lbs so she will be rear facing awhile. Do I want a rear facing that teethers? Is it necesary? I'm looking at the Radian 65 but I hear that one is hard to install and it will have to come out alot to put in Grandmas car (since she dosen't beleive in keeping rearfacing past 1 so she won't buy a rear facing car seat) and the Fisher Price Safe Voyage. Would I be better off paying extra for the Marathon that teethers?