Tried this stuff a few times last year and will never touch it again.
I am very experienced with stimulants, and have tried pretty much every RC and illegal stim out there, and this stuff gave me the most unpleasant comedown and after-effects of any of them.
Doses from 30 mg to 50 mg provided maybe an hour or two of pleasant stimulation followed by several hours of anxiety and tweakiness.
Doses from 100 - 150 mg provided a 3 - 4 hour, super-speedy, quasi-MDMA esque roll which quickly faded into stimulated anxiety that lasts 12+ hours and keeps your pupils dilated for up to 24 hours. I did a full dose like this twice, and both times I experienced the most hellish, suicidally depressing comedown I have ever had. Makes the MDMA crash look friendly and fuzzy by comparison. Felt like I had a serious flu, muscles were fucked, and it seemed as if all the happiness had been drained out of the world. Also, for 2 days following the dose, I experienced 'brain zaps' when standing up or walking that made me feel dizzy, as if I was about to pass out. Very worrisome symptoms all around.
Even Desoxypipradrol and MDPV, which have both fucked my head into complete psychosis in the past due to lack of self control, have an easier comedown than this stuff.
I'm not trying to dissuade anyone from trying it, because everyone reacts differently to these compounds, but I wanted to share my experience. I'm sure I'm not the only one who has had this reaction from 4-FA. Be careful!