Flexington
All Star
I've done two playthroughs at this point with a total of over 200 hours
And I haven't used a single blade oil.
Do they do anything worth the use cost? I've used poison twice, but even that seemed iffy. How you finding them
I only used them a lot due to my character being a rouge/thief. I usually craft them. Some are more helpful than others for sure, like drow poison/ones that inflict silence, blind or sleep in addition to disadvantage on attacks. Accuracy helps for sure too, Laezel was having 30% to 60% chance on attacks but after the accuracy oil it shot up to 70%-90%.
Effects like basic poison are kinda eh on their own, but there are higher grade toxins that do more damage. Wear some gear that stacks the damage and have bonus actions/action surge and it can get crazy.