I'm guessing the name you're looking for is Valerylfentanyl. Sometimes called Pentanoic Acid, or TCE, which are both very inaccurate names that refer to very different chemicals that are about as far from something you'd want to consume that you can get. I'm guessing the name "Penta-fentanyl" came from the misnomer Pentanoic Acid. I'm still really not sure where the name TCE came from.
As for discussing the chem, it's basically Butyrfentanyl with an added carbon.
So lets talk chemistry and neurochemistry. To make the drug legal again, they have to add the carbon (or something else) to the Acyl chain. The Acyl chain is very important for mu-receptor activity (aka the good opiate effects you're looking for). For chems to be activate mu-receptors, they need to be able to bind which means they need to be able to fit. Basically it's like you're trying to fit a puzzle piece into the receptor to match the receptor's shape. The reason Butyrfentanyl is so much weaker than regular Fentanyl is because it's a modification of Fentanyl's structure, one that fits well with the mu receptor agonist. In this case by replacement of the N-propionyl group by another acyl group (by the normal analog nomenclature, regular Fentanyl would be called Propionyl-Fentanyl). This means Butyrfentanyl doesn't fit well with the mu-receptor. Some people still buy it I'm sure, but from what I read, it's basically a waste of your money.
Now take a step forward, and they've added a carbon to the Acyl chain on Butyrfentanyl, so this will make the fit even *worse* than Butyrfentanyl, which is already weak enough. So my guess is that this analog will be very weak, and require a significantly higher dose to get the usual opioid activity. Although the required increase in dose to achieve the positive effects also means that there will be an increase in negative side effects.
Now that's not to say I'm right. I don't have a degree in chemistry nor neurochemistry, and I don't think even those who do would say with certainty without research if the effects are more/less/equal, but that's my educated guess.