Carefresh is definitely better than sawdust
However,there are better substrates than Carefresh.Fitch for example in the UK is nowhere near as dusty and would cause no allergic reaction(sawdust and other things like hemp can and often do,especially in the case of wood based substrate).It's also cheaper than Carefresh even though it might be awkward figuring out just how to store it at first(the 20kg size is the best value).