I actually have tried it once, and after my suspicions havent gone back, it was my first time rolling so I have nothing to compare to - it lasts a long time, but the euphoria and such is pretty quick, maybe an hour or so tops, after that it just feels like stimulation, you're still talky and such, but the initial euphoria is gone - also, the not bitter thing is really what had me scratching my head - it is bitter, but not in the way I'd heard MDMA talked up as.
it also doesnt really hurt to insufflate, at least the first couple lines dont, and ive heard MDMA can be pretty brutal on the nose.
Most of what you described about this drug suggests that it is almost definitely NOT mephedrone. Mephedrone is fabled in the amount that it burns to snort and is thought to be only short of the burn of the 2C-x compounds and a couple other odd compounds. Pure MDMA powder actually hardly burns at all generally, if it is crushed and not in the form of small sharp needles. Mephedrone is actually fairly bitter and should be on par or more bitter than MDMA. Actually, if you get rather pure MDMA, you'll notice that it's not all that bitter compared to most things. It actually has a sweetness to it, reminiscent of sassafrass and doesn't taste that bad at all. Usually really bitter "molly" is not pure MDMA but mixed with other, more bitter compounds, or just other bitter compounds without MDMA, which often burn far more than MDMA to snort (especially, like I said, mephedrone, which is REALLY bad. It's strange because, unlike almost every other related compound, which only really burn when snorted if at all, and which are bitter on your tongue, mephedrone actually seems to be highly caustic to all bodily tissues, including the tongue, nose, lips, throat, stomach, anus, and even your skin like on your fingers). In addition, mephedrone is very short lasting, only producing a considerable amount of stimulation with a reasonable oral dose (which lasts much longer than an insufflated dose) for about 2-3 hours with a quick come-down. A snorted dose of mephedrone lasts about 30-45 min with a fast and unpleasant comedown accompanied by high craving for another usually, whereas with MDMA, a snorted dose usually lasts about 2-3 hours. What does correlate with your description is that mephedrone's euphoria sometimes only lasts for an hour or a little longer, with persistent stimulation afterwards until coming down, and that mephedrone requires a much higher dose than related MDxx compounds and is often consumed in >1 g per session.
Short but strong euphoria then energy - sounds like Mephedrone to me. I always feel wired for a good while after taking it and it's really moreish so 2-3g a night isn't stupid amounts. However I find it to be REALLY euphoric and when it's from a good batch it can be close to MDMA (apart from duration). But they're many things it could be.. only way to find out is to test it.
XTCity, the OP said that it is long lasting, not short. Also, yes, mephedrone is very moreish, but 2-3 g in a night is a very stupid amount to take. It's not unheard of no, nor is taking 1-1.5 g of MDMA in a night, but they're both highly stupid, especially since there are plenty of accounts of some pretty damn serious and terrifying health effects from 0.5-1 g of mephedone in a session, including blue skin and foot-drop (loss of muscle control of lifting the tip of the foot towards the ceiling).
Now for a bit of my own personal experience: I have noticed and some agree, though not all, that mephedrone has a pretty bad comedown after taking a pretty strong dose, ESPECIALLY when it's snorted, and especially with redosing. There's pretty strong disagreement about comedowns and hangovers from MDMA, but many people strongly believe and experience that a single medium to strong dose of rather pure MDMA has very little comedown or hangover except for some exhaustion and a slightly dulled mind for a few hours to days. Generally the intense comedowns and hangover effects that last for days to weeks and cause strong depression and memory loss are associated with very high doses of MDMA, redosing, and especially with MDMA or related compounds mixed with relatively pure stimulants like amphetamine or methamphetamine, which are thought to also greatly increase neurotoxicity and oxidative stress. Most people I know and from personal experience I say that a reasonable (even strong) dose of relatively pure MDMA has essentially no comedown and I feel perfectly sober and ready to drive home and I feel fine to great the next day, with maybe a little lethargy a couple days later if anything.
Additionally, MDMA makes many people, including myself, sweat profusely, as it is a strong stimulant. Also, some people, again including myself, find that MDMA is not that strong for them and that it is essentially just a nice stimulant with some euphoria that doesn’t last that long, and some people only have euphoria that lasts for an hour or so with moderate to strong stimulation (or no effects) after that. The fact that these people are taking this drug every day suggests that it is at least in part composed of a pure stimulant, which tend to work over extended periods of consistent use (albeit of course with tolerance and decreased positive effects) much better than MDMA, which rapidly produces high tolerance and even desensitization to the extent that no dose can produce the desired effects. Your descriptions overall sound like the effects of a pure stimulant, since (meth)amphetamine lasts for 6-12 hours and you said it’s long lasting, and since these drugs tend to produce euphoria that only lasts about an hour or 2, with residual stimulation lasting for many more hours until gently petering out when taken in reasonable doses. Of course the doses you described don’t make any sense for any of these drugs but mephedrone, but it’s highly likely that the drug is composed largely of fillers like talc, maltodextrin, cornstarch, etc, which would decrease the bitterness. Also, amphetamine and methamphetamine aren’t particularly bitter in their salt forms, and would not be very bitter at all if diluted 10-100 times in cornstarch. What form is this drug in and what does it look like? Is it powder or crystals; what type of crystals if so? What color is it? Also, how long would you say a standard medium strength oral dose lasts?
Sorry for such a long post, but I hope this helps. Also, just because some people use ridiculously huge doses of drugs does not make it safe or ok, or even that it would turn out just fine for you. Everyone has a different sensitivity to each drug and tolerance likely is a huge factor in the massive doses your friends are taking. Just remember to be extra cautious when approaching an unknown drug.
-Jaguraguguru