I respectfully disagree with the "everything should be fine" comments. Remember, this is a MacPherson strut set up, not a double A-arm. In a Mac set up, it's the strut that maintains the geometery of the steering knuckle. Remove the strut, and the knuckle flops around. This is not the case in a double a-arm. In that case, remove the strut, and the knuckle maintains its geometery (like on a Kia Sporty). The strut shaft in a Kicker sees forces both longitudinally and laterally. Longitundinally, it's not a big deal, but laterally puts the extender in a stressful condition. The pic I saw of a cracked extender seemed to be caused by the lateral force I mentioned.
If it were me (and it isn't) I'd add a strut spacer, or flip the stock mount. It's not like the extender adds useful travel.