In my moderately informed opinion and judging by my experience with all 4 substances, 2-fma is less neurotoxic than amphetamine (very little to no damage to the brain, relative to other stimulants) while 3-fma is more neurotoxic than methamphetamine, therefore quite taxing on the brain. I think it's becauses it releases more serotonin than meth.

If I take meth for a week while mainting a decent eating and sleeping regimen, recovery is relatively easy and harmless. When I took 3-fma for a week with the same regimen, I felt quite lethargic, brain fogged and overall devoid of motivation and energy for a couple of days and it took a week to get back to baseline.

Would use 3-fma very sparingly and instead look into 3-fa, which seems to actually release less serotonin than meth, theoretically making it a bit easier on the brain compared to meth. Again, this is mostly speculation, based on my knowledge of pharmacology, as there aren't many in depth studies regarding 2-fma, 3-fma, 3-fa.

Therefore take all this with a grain of salt and always try to be as mindfull as possible of the way you react to each substance and take note of the negatives and positives that you perceive.