A.W.
RF is the safest way for you child to sit as long as he is within the weight limits of the seat, if he has outgrown his infant carrier then you can get him a convertable seat and most convertable seats will RF till about 30 to 35lbs (depending on the seat) even if he is tall its still safer to have him RF and yes like someone said, it is possible for him to get a broken leg in a crash but there is a greater chance of a broken neck if he is forward facing and a broken leg will heal but there is nothing you can do about a broken neck. my DS is 23 months old and 27# and 36 inches and he is still RF in his Cosco Scenera http://www.walmart.com/catalog/product.do?product_id=5716972
which was only $40. after he outgrows that seat we plan on getting him a britax regent which will keep him 5pt harnessed till he is 80 lbs.
if you have any other questions feel free to send me a message