whichever route you go opt for the lower temperature-actuated fan switch (goes into right hand side of radiator)
this helps keep the temps down for sure- fan comes on sooner, but doesn't stay on long as it the engine/cooling system has accumulated less heat to shed. Without the sensor change both fans will run but run much longer, which (assuming you are riding slow/offroad which is where the additional cooling is REALLY needed) will be hard on your battery as the alternator isn't spinning fast enough to keep the voltage up.
I used Ken's AdvMachines kit as that's all there was at the time- and while saving a few bucks is always nice I'd rather give my $ to ADVRider-supporters (both BDCW & AdvMachines) and not somebody out of the loop.
If you do go fleabay then consider donating
to ADVRider itself, Baldy is one hell of a guy to have created & hosted this site for us for years & years, all at his expense