This is a simple remix of eried's original "Beard shaping tool" where I've made the curve a little more shallow which better fits the hairline I'm looking for with my own beard.
I also noticed the comb bristles were a tad fragile on the original. On my first use, I held the guide by the comb area and snapped several under my meaty thumb. Here I've shortened them a bit and gave a little more reinforcement where they attach.
Now trim yer beards ya scruffy bastards... :)
I printed at 15% infill with 3 top/bottom layers and it's fairly rigid. You might want to bump up your infill to 20-25% to make it even stiffer.