No, I don't use it, and I find that 5e offers plenty enough rules to make combat interesting and dynamic, even though the rules are quite simple. You can duck and cover behind something, stand up, shoot an arrow, and take cover again. You can move toward the enemy using a dodge action, making it harder for enemies to attack you as you move forward. You can use an assist action to give a teammate advantage on their attack.
You can really do anything you want, and there will be an ability check to see of you succeed. Jump over a table in a tavern and smash a chair over the head of a large, burly half-orc who started a fight? Go for it. There are enough abilities and situations that grant advantage already that add to the dynamism of combat. And if you grant advantage to flanking all the time, you might make certain special abilities, like rogue's sneak attack, less special, and at the same time you will train your players to think in "accounting" grid-battle more than dynamic story-telling battle.
I use that word, "accounting," a lot to explain my central thesis that roleplaying is all about telling a story with your players, and that the rules should serve that purpose, and not become the master. The grid, too, if you use it in battle, should also serve the story and not take the spotlight away from the story. When players concern themselves always with trying to position themselves on the grid just perfectly for flanking, it cheapens the storytelling of the battle scenes. (Plus the PCs in 5e are plenty powerful enough without extra flanking advantage.)