Have you ran one these? My cheap one is fine. I had it next to a pwr one and for the $700 price difference, there aint a lot of improvement with the PWR one.
No i have not run a alloy one, but when mine split i looked into my options and spoke to several people (performance places and just rad supplyers) and they all said the cheap alloy ones where not that good and one place said they had seen them fail with a small head gasket leak.
I also wanted the heavy duty one thats 26mm over the standard 16mm (or there abouts) and i also was told they are crap and not to expect anymore than 2 or 3 years from them.
Yes the good quality alloy ones are good but you pay to much for them, a good plastic one will set you back less than $250 just for the rad its self and seeing you pay $800plus for a alloy one its just not worth it in my book