I had the Graco one for Jack in my dads car and i agree are very bulky and heavy
I had the Mamas and papas viaggio thing for Jack in our car but i got it cheap with the pram from someone, i understand they are Very expensive usually, it was still a bit heavy though
I would say though that if the graco is still in good condition use that if you can manage with it, think of all the extra cash you will have to spend on other stuff

Sorry not much help