Unfortunately CFM numbers are basically meaningless. It depends on the length of the run, how many turns, diameter of the duct, and the type/quality of the fan. it also depends on how vigorous the boil is. Given the extremely low price I would not expect anywhere near the rated CFM other than if the fan was blowing with absolutely nothing connected.
Does that mean it won't work? No, it just means that unless you get mech specs on the fan and how it behaves with duct loading, it's a guessing game.
For an electric based brewery a good rule of thumb is to divide the element size (in watts) by 17.6 to obtain the required CFM (cubic feet per minute). In my case I use a 5500W element in My boil kettle. 5500 / 17.6 = 312 CFM. I therefore require a fan that can move a minimum of 312 CFM in order to ventilate our electric brewery properly. Fans this size are readily available and reasonably inexpensive, you just need to make sure that the rating doesn't drop well below that once you add ductwork.