Parafluoroisobutyrfentanyl must be rare as fuck, since i find no experience reports or other information anywhere, which is the same with places selling that incredibly lovely (and incredibly dangerous!!!) substance.
I had the chance to try a sample (50mgs) some months ago but unfortunately never had the chance to aquire more of it, so if no one spreads information about it, at least i can tell a few things for ppl interested in it.
So it is BY FAR (honestly, BY FAR, FAR FAR!!!) the most potent Fentanyl Derivative there is, has an exceptionally long duration and extraordinary broad-spectrum effects-profile and has (at least when dosed rectally) a ridiculously fast onset, which means in detail:
Potency: it's a fuckin' TERMINATOR, honestly... I cannot name detailed numbers, but it's the strongest among all the F-Derivatives, and 1mg means overdose for most ppl (and yes, even those with a high Tolerance to Opioids/Opiates, and i've taken Hydromorphone for the past 7 months and am back to Oxycodone now, as i'm chronic Pain Patient and took doses of 80mg+ HM (plugged) or equivalent doses of Oxy without having ODs, i.e. those are my exceptional recreational doses if used (sparingly) for this purpose. See ONSET for a few other related infos about POTENCY!
Duration: it's hard to determine, but as far as i remember, effects are felt at least till the 6h mark, perhaps even longer (as i don't remember exactly, i won't name detailed numbers, again, as i don't wanna spread false data, so rough estimation is the only thing i can contribute - which is giving a good picture, even if not perfect, about this rare Compound and it's profile). What i can say is, after researching EVERY single one of all of the Fentanyl-Derivative RC Compounds, with the sole exception of the possibly toxic Acryl-Fentanyl (i don't wanna ingest Acryamide, not even in lowish' doses!), that Parafluoroisobutyrfentanyl, had the longest duration of effects compared to the other ones, just as is had the most full, or more precisely, broad...
EFFECTS-PROFILE: As said, PFIBF felt "full", it wasn't as (subjectively felt) good, or full-spectrum Opioid/Opiate-effects providing as my personal Favorite Acetyl-Fentanyl, which had the warmth and subtle euphoria of even classic Opiates like Morphine (to a degree, not totally, but to a degree, at least), but i rate it very high and it felt not sterile, or cold, but somewhat full and absolutely on par with stuff like Hydromorphon/e or Oxycodone (but that's just me, and i should point out that not one of those two provide euphoria to me, that's exceptionally the case in 1/10 times dosing O-DMT or, as it is totally outstanding for it's unrivaled Effects-profile and the sole exception Compound of this Class, which did this more than just once, i.e. providing euphoria (not in-your-face, but through muting my Pain-issues strongly, a subtle, trance-like and impossible to describe feeling of what i would call euphoria). But to feel it's effects, one must (and it's not easy to handle!) dose correctly, and be prepared (to not get wiped-out High-Kick Style) for a very fast...
ONSET: which is (i just dosed rectally) fast as fast can be, and it did hit me not just once like a plank (honestly, it REALLY felt like a plank, full-frontal...) in the face, and even if handled properly i ended two times in the corner of my kitchen, woke up after 2-3hrs as it came on way too fast, or better, way too far as expected (that was the first few times i tried it) and i think, if i remember correcty, it was for sure (!) under a minute, i'd say 30sec. at most, and i do know exactly that i didn't even had the chance to put the syringe and PFIBF containing flask aside, and this means something.
So that's it, i hope it helps someone to see that it's one of the best of this Derivatives, within my personal top 3, but also the most dangerous one to handle, even in the right hands... Stay safe ppl!