I find it very useful in the raid, but for the raid only. Other aspects of the game, I'm better off using something else
With that being said, not [i]every[/i] part of the raid is the ToM useful. For Warpriest and Golgoroth, I like using Boolean Gemini because it is a versatile scout rifle. ToM is good for Daughters and Oryx Encounter
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If you have the raid sniper and max regen, you can ToM down to a sliver of health, switch so sniper, pump a few rounds in and switch back. By then your health will have recharged a significant amount and cocoon will reload for you while you ToM again. Consistent reliable dps. Works on all bosses ever really.