
The only drawback is the creature trying to break free. Due to the clause that the monster randomly attacks targets when not controlled and lasts for 1d6, even if you drop or lose Concentration during combat you generally get to have the monster hit things until the end of combat. It gets you non-Concentration utility too. This is Polymorph-levels of extra HP to the fight. Nothing compares to the Babau far as durability goes: resistance to non-magical weapons + 84 HP means it's basically just not going down to anything your enemies can throw at it unless the same attack would kill PCs of the level in one shot. Both Babau (at-will Dispel Magic, Heat Metal, Darkness, Fear, Levitate - a potent spell list even for a spellcaster, essentially a Wizard buddy) and Barlgura (Phantasmal Force, Entangle & Invisibility with surprisingly decent save DC) bring good spells to bear. And also in environments that are naturally sight-limited, of course. Darkness-users in the party, your own Pyrotechnics or anything of the sort. Barlgura also has Blindsight which is great in conjunction with e.g.


Barlgura in particular has 3 attacks at +7 with advantage for 31 DPR. It gets you the hardest hitting things. Summon Greater Demon and it's not particularly close.
