Just make sure you know the Wattage of the size flex you are getting. and youll be fine.
To my knowledge, these are the most widely available types of flex you can buy.
3" flex is 10 watts per foot.
11" is 20 watts per foot
4" is 8 watts per foot
Anyone can add on to that information, of course.
It seems to be wiring that was purchased from a hardware store. If you arent sure about wiring, you can email clay from his website, to ask him any information you might be interested in knowing. hes really helpful.