So there was a very similar trinket in Legion: the Royal Dagger Haft. And pretty much everyone said the same thing: it was crap, never use it, etc.
The reasoning was usually something like… “it can only trigger once a fight, trinkets that can help you for the whole fight are better.” Or, “if you’re dying, then you (or your healers) are doing it wrong anyway.” Or… who knows what other logic people use. Most of the arguments (like those two) were very flawed. Maybe there is a better one floating around out there too… haven’t really looked.
Short version: we disagree. For most players trying to improve their toughness, Bwonsamdi’s Bargain is simply the best trinket out there. Similarly, talents like Purgatory are very powerful. These things really shine when you are learning new fights, and you or your team might make mistakes more often – it’s a free pass in a fight when something goes wrong: you time up a cooldown poorly, or a healer dies and things get messy, etc.
Once you have fights on farm, or you feel pretty tough and rarely find yourself close to dying, then sure, swap it out for something else. That goes for toughness-oriented trinkets and azerite powers in general though – many players prefer to shift into things that are more DPS-oriented as they gear up, or things that have hybrid benefit (e.g. stat procs have both offensive and defensive value, whereas an absorb proc is only good for defense, so as you get tougher, you might shift away from an absorb trinket/power. The toughness threshold on the optimizer can help with those kinds of choices).