when you put LED lights in where iridescent lights were the cars system thinks a bulb is out because the voltage isnt enough, resistors essentially trick the car into thinking nothing has changed. in some car you get a bulb out warning on the dash, other cars you get hyper flash, and people have reported some LED bulbs just not working at all because of the cars system. Its more cost effective to wire in the resitors yourself if you have general electrical knowledge about a car, resistors get hot so mounting them to plastic is a bad idea.
6 ohm is a little low for turn signals, but those are neat. I plan on making my own kit though and doing the soldering and heat shrinking myself. I used the 25 ohm load resistors myself since those oughta do the trick, but if they don't work I'll probably get the 6 ohm ones.