Whats the advantage of buying a nice oil catch can from just making one out of a fuel filter? Is it just cosmetics and a larger canister or is there something more to it?

 

the only difference i would see from a nice catch can to a "homemade" catch can is that some nice catch cans have extra features. some nice catch cans have indicators that tell how full the can is. I have also seen some catch cans have release valves that make it easier to dump the oil. as for catching the oil, homemade catch cans work just as well as nice catch cans.