If he has a 42" tank the 48" MH
will not fit from odyssea. If he got a 36" it might not be enough AND it could melt one of the support beams, if he has one.
In total honesty, I would avoid these fixtures if you can, I know the price is super cheap but you really do get what you pay for. The 2 T5 odyssea fixtures I have/had were very reliable but also very cheap. The newer T5 setups are pretty tinny and cheaply made.
Have you checked into a pendant system maybe? You could hang 2 MH