They're basically made the same way as a Greddy/HKS/Blitz...tube and fin design. As long as they don't leak and the insides of the entanks are smooth, they should perform almost exactly the same. Only thing you're losing will be some of the ease of the install. The ones made for the S chassis come with good instructions and lots of parts.
I'm going to get a bar/plate eBay intercooler and have piping made. I figure I should be able to get it all done for less than $500...maybe even less than $400.
Get the off brand unit. Save yourself some cash so you can buy something else more important...like brakes or tires or something. $800-$1000 for an air radiator is a rip. Well, at least considering what you COULD get for the same money if you bought some Spearco parts and made the whole thing yourself. That bish would be HUGE! And good for like 600 hp with about no loss.
Eric