I remember now that Carfentanyl has been used as a chemical weapon by the Spetsnaz during an hostage situation inside a theater.
They pumped it in the building's ventilation system to knock out everyone inside.
Of the approximately 900 people inside, between 131 and 300 people died from it (the government covered most of the aftermath in secret) and the terrorists didn't get a chance to even shoot one round before they collapsed.
You are not likely to survive handling pure Carfentanyl, and even if you did manage to use it without diying, your tolerance would skyrocket and you would not be able to use heroin.
Also, if you die while you handle Carfentanyl, you are likely to leave the drug in one form or another lying around, endangering whoever finds your corpse like friends, police and paramedics.
Finally, getting arrested with it would most likely turn into the maximum sentence conceivable for possession of drugs with intent to sell as you would be in possession of thousands of doses of a very deadly drug.
I would consider sourcing heroin from another street or DN dealer a much safer option.