What does he want out of a cat? Quick pros and cons:
Pros: cheaper on fuel than the Fibreglass cats, cheaper to tow, better transducer placement for sounding, can customise easier than fibreglass builder and quicker build times. smaller donks needed to push boat so cheaper than fibre.
Cons: galvanic corrosion, paint issues over time, due to lack of weight probably a slightly firmer ride than a KC or NC, lower re sale value than KC and NC. Will be subject to stress fractures over time.
I just went through this myself and ended up with fibreglass due to end resale value and better ride...