There is a ton of information in the forum about this subject. I have been researching the same thing. Many say stick to the OEM style mech fan, some switch to tarus fans with significant cooling power and a big electrical draw, and others like trhe mech fan with a clutch. I think its a trial and error thing and might be sort of a personal preference.
Here is MY short version of what I have learned through searching - Electric can leave you stranded if it burns up, shorts, etc and can't be run underwater, but you can switch it on while the truck if off if you over heat and drop temps enough to limp it home. Also don't take the CFM ratings literally as they are rated assuming there is no resistance - like open air. Once you put em behind the radiator the numbers drop a bunch. Mech. runs all the time and supposedly robs the engine of potential power and might inhibit cooling at high speeds. Clutch fan will fix the high speed issue with mech. fans as it will turn off allowing more air flow at speed.
Another thing to consider is the shroud and fan placement within the shroud.
I don't have any experience with the Derale fan your asking about but would be interested in what others say. I'm going to try the electric fan route first myself and resort to other means of cooling/fans if this proves unsuccessful.
good luck!
