I have extensive experience with phenibut and a bit with fluorophenibut. f-phenibut is substantially more potent, it kicks in faster, lasts much shorter, and is more intoxicating, but less good of a drug IMO. It's not too much like phenibut, it's closer to a cross between baclofen and GHB, that is, less euphoric than GHB and less wonky, too. Heavier on the GABA-B side of things.