I have used 5 gram 3-FPM over the course of 3 weeks on pretty much daily basis.
I had 3 'big sessions': 2x 500mg over an evening and my very last 2,5 grams at the first 3 days of a festival, was awake for 80 hours then. Never thought I took so much, just kept filling Rizla's. Yeah, dumb

But I was amazed I was still behaving and feeling quite normal towards the very end of those 80 hours, I just came home, stayed up for a couple of hours, checked a few things on my laptop and just went to bed. The time between the last dose and falling asleep here was 11 hours.
I experienced following effects:
Minor headaches, only when re-dosing and not getting sleep, it went away fairly quickly with a single beer though..., Minor visual distortions such as little black spots, I first thought were flies in my room, colors shifting, colory thingies in my peripheral vision, plants slowly waving, etc... but nothing scary. These were becoming apparent for me after the 3th day mark, didn't notice much of it with 1 night of no sleep. As a matter of fact, as i'm typing this now objects around me started shaking furiously like I've never seen before. :D Haha (Been up since monday morning, with 4 hours sleep on sunday night, no drugs except LOTS of coffee, lots of tobacco and an unhealthy amount of stress involved). I got back-outs after about 75 hours, when walking home It felt just like I teleported from point to point few hundred meters apart till I got home. But isn't that also due to the sleep deprivation? Didn't had much trouble making conversations at all during use, spend hours talking interesting subjects to strangers. Even at +-70 hours awake I was having a really good 2 hour conversation with some Christians that interpret the Bible literally. I don't know a damn about religion, I don't really give a damn about it too, but it was super interesting for some reason, and they gave free coffee

That really helped me. Losing track of time also occurs when re-dosing fast after each other. Sometimes I had a stinging feeling that didn't last longer then a few seconds, could be from sitting down in the same position a long time cause I never notice that feeling when I'm outside and/or moving around. Once I had a pulsating vein in my neck that went normal after a sleep. No muscle cramps. No paranoia ever. Then haven't used it at all till 4 weeks after. I never had a crash from it, I think, and if I had, the crash for me must have been not that bad. The first day after stopping, I got a stomachache in the evening, that went away as I got home and I did got tired fast about till 3 days after but it had planned Modafinil and MDMA (150mg) the remaining 3 days of the festival so it wasn't a problem. For the modafinil, just one 200mg pill should make me feel like I've had a super good quality sleep but I took 600mg to feel anything more awake, in the afternoon, and I could fall asleep easily not too late at night, so yeah,... I did feel a typical mdma crash for 2 weeks, but it wasn't worse then any other. Never got the mentioned flu symptoms eighter.
After my experience, no drugs were taken besides some glasses of wine/beer and a few joints here and there for 4 weeks.
Oral is my favorite way to go, I find the effects more balanced and I think the negatives are less pronounced and stay out for longer when redosing (not sure might be personal).
Snorting on a big sesh left me cleaning and picking out bloody snot out of my nose for a good while and had 2 days the feeling I was walking around with a super strong Vicks in it, so I'm not doing that anymore
Oh, and this is my first post! :D
After lurking around here for a good while gathering information for myself I tought it was my turn to give something back, hope it can be usefull!
PS: I red through a lot the recent posts today, lost this topic out of sight last weeks, and I'm going to be more careful with the substance in the future. At that time my information was: 'highly functional,...blablabla stimultant' shitty drug.
This is my first stimulant, besides from MDMA then, so I can't compare it to something else. But I knew this had more potential then being a boring straight stimulant during my big sessions. Had mdma-like feelings towards music, chatting with people (although not in the mdma softy way), complete with very mild bruxism, sensitive touch and colors becoming brighter. It lasted for about 20 minutes I think, but it was there at some point, very clearly.
Oh and I also have to note: During the last week with my 2,5g and mdma, I forced myself larger amounts of food. I ate a larger amount of meat then usual as I felt I could use the proteins as I was moving around all the time. Yet it was easy for me to see I lost a fair amount of weight.