That is a great mounting location for lights. Here are some pros and cons I've found over the years...
Pro tips
Set the middle two to fill that dark spot in your high beams that the lows usually fill. They also work great at increasing the contrast of potholes and road textures (everything from rocks to standing water) to make night driving even safer. Easy to wire on a relay. Another is that unlike over the roof light bars they don't hit low branches.
Cons
It is also a very dangerous for the lights so give them adequate protection. They'll be eating bugs, dust and whatever the car in front of you kicks up. Rocks and stuff cracking the lenses are a problem for me.
I also use my brush guard to pull and push objects so I have to be careful not to put pressure on the lights. I've already broken one set by forgetting they were up there...But since you probably don't use your truck as a bulldozer it shouldn't be a problem.
Overall, in the words of the TMC staff,
DO IT or you are contributing to the pussification of America!