Compared to (moderate-high dose) MDMA, meth, and even coke comedowns, mephedrone doesn't even have one [even at high doses], it just brings you back down to normal and wanting more.
And i agree with OP, if you think Mephedrone feels anything like your run-of-the-mill stimulant, you were given something else as i can binge on mephedrone all night and sit in the same spot not doing a damn thing.
I don't think any of us are in the position to say just how neurotoxic 4-mmc really is. But generally speaking, any stimulant you take will have some damaging effects to (at least) your serotonin and dopamine, i suppose the real question is how toxic it really is and compare to other stims. You can't base the toxicity on color, smell, texture, and corrosive characteristics.
One major concern i have about this particular substance is cardiotoxicity. It seems like it's worse than (good clean) cocaine from my experience just by the way it affects my heart, breathing, muscles, blood pressure/circulation. Though it may not be 4-mmc itself, but a metabolite of 4-mmc from liver processing...
Edit:
On a subjective note, I would compare mephedrone to MDMA... it's the closest "mainstream" drug to give a description. However, MDMA still has vastly more powerful and, seemingly, less dangerous side-effects. I prefer mephedrone over mdma only because the high from MDMA seems so "pushy" to me. Mephedrone seems to make me think i'm more in control of what's going on. However, i hate mephedrone for it's cardiovascular side-effects and coke-like moorish personality... as well as it's short-lived high.