I was given a Bandit SX-135 weed whacker a couple years ago and it works great but the head was awful. It always clogged up with grass, broke lines, and took forever to extend new line.
I bought this Shark Tooth model with the serrated lines and it’s great. The lines last a LONG time, they can cut through a black hole, and are easy to replace. Replacing the stock header was trivial too. Highly recommended.