If you don't know the actual names of these compounds then you shouldn't be going anywhere near them.
These compounds should both just be avoided altogether. I can easily see this new trend toward fent analogues ending very badly - either with mislabeled "heroin" products being distributed to unsuspecting buyers (just like 3-methylfentanyl throughout the 80's being sold as "china white" and leading to a rash of overdoses, some fatal), or with another neurotoxic impurity as was seen with MPTP (which caused a permanent state of parkinsonism in a few unlucky consumers).
Anyone who does run across these compounds should be extremely careful, they should NEVER be used without precision measuring equipment. Both compounds are believed to lie between fentanyl and diamorphine in their potency. Always be aware of your state laws (not to mention federal law) pertaining to both. I will never condone breaking the law.