At the end of the day, methyl versus dimethyl, you can't stand on solid scientific ground saying one is measurably worse than the other. Caffeine, if I'm not mistaken, is a dimethyl compound.

None of it is 'good' for you. It's just a matter of running it responsibly and taking precautions to minimize damage. This is an adults only, no rules/no guarantees kind of game no matter which way the hammer falls.