Firstly, external coolers are usually loud.. adding twice as much noise when tacked onto your system. Case and point my Xbox 360 sounds like a lawn mower now thanks to a thirdparty cooler. Really ruins the gaming experience as u get distracted from it! Secondly, external coolers usually drop the overall system temperature by a 2-3 degrees. Not a big significance if you already live in a cool and ventilated area. my 2cents.
Absolutely pointless spend of money, better to pay for good cleaning service and good thermal compound and change it regularly so temp stay nice and low and same with cleaning do it regularly with compressed air