I've never done 4-MEC but I have lots of experience with 4-MMC. 4-MEC is probably slightly more neurotoxic than 4-methylmethcathinone (4-MMC) which, from experience and other reports, isn't toxic enough to cause any long term damage if used responisibly. IME 4-MMC feels really cardiotoxic and I assume 4-MEC would be too.
There hasn't been enough real research done on this drug to know exactly how toxic it is. You just have to go by other peoples word.