I would say you need a filter anyway because it helps get fresh air in and old air out. A carbon add on filter will get rid of the smell on the air being removed.
if your venting to outside then yes i would say you needed to get one. I would recomend Phat soon to be called Rhino filter.
go on to ebay, type in carbon filter in the search, they have a few , I just bought 4inch inline fan with 1 m of ductint and a carbon sock for £60. Bargain man trust me
That guy works great for very small area's, should work good for yours. You can use it as a small exhaust if you like as well, as long as you have a small area. I just keep mine the the room to scrub, them I have a cheap homeade carbon filter at the exhaust.