I learnt the hard way when purchasing VN Aluminum type heads on Ebay. Some sellers claim their Aluminum VN Heads are rated at 480hp out of the box and with a little TLC they will reach 600hp. We brought 2 pairs however out of the box they didn't even out perform standard cast iron VN type heads. Both sets flowed around the 400 hp mark. Compare this to a set of untouched cast iron heads where you get about 430hp. After many dollars and hours we got them up to 500hp, no where near the claimed 600hp.
When purchasing these heads I guess you have to weigh up the cost of cast iron heads ($250-$350) compared to these Chinese copies at ($1000). Yes the chinese heads are lighter and may disperse heat quicker, but you will need to spend ($800-$1000) on porting to get them up to the HP they claim. CNC porting will cost you around $1500-$1900 so choose carefully.
Hope this helps.