The TRD kit would seem more expensive because of the cost of the kit, however when you take into account that there is no other kit that fits perfectly, you save quite a bit on the installation, plus they are made out of urethane instead of fiberglass. I have TRD side skirts and rear valances with a Black Widow front bumper, however the entire TRD kit would have been about the same amount with all said and done.
As far as the durability of fiberglass, I have a Black Widow front bumper that has gone through many scrapes driving on the worthless roads in Missouri... So I try to stay in Kansas

It has held up for about 3/4 of a year now with no damage. Impacts to a fiberglass bumper will not be as forgiving as a normal bumper, however, even at low speeds. I've never had problems with pot holes, it's the steep inclines that make me cringe hearing the bumper rub.