Well seeing as the reason for it's creation is a synth opiod - but only less fun (addictive). I'd say based on that alone it has to suck and that it's been taken off the s II roster of meds (in the US).
I see its apparently unscheduled. As potent as morphine as an analgesic, but I'd want to know more about its effects on mu receptors, it's not a full agonist, of course, but what is its efficacy compared to morphine at activating mu receptors?
Don't ever take it with H or if you are on methadone... it'll send you directly into withdraws but if you have given up H ... it works good IM for pain.