I once very sloppily attempted to IM some methylone, along with ketamine in the same barrel. I was already on IM ketamine and very high on cannabis so I can't quite remember my train of thought, but I did 100mg M1/25mg ketamine... It took about 5 minutes to kick in, and it was a short lived, but intense burst of the typical methylone euphoria with a little hint of k. Walking wasn't the easiest but very do-able, as I do remember walking outside with a joint. There was more of an introspective focus to the methylone stimulation, rather than the desire to socialize that methylone brings without the ketamine.
I imagine IM M1 to be fairly ineffecient as the duration of the high will be decreased, the fiendy-ness of methylone to re-dose is even stronger and (at my dose) qualitively, I could not notice much of a difference in intensity.
I would think IVing the methylone would be much more worthwhile (in addition to infinitely more fiendy) but for the sake of harm reduction I'd say try plugging if you're looking for an alternative RoA for methylone.
EDIT: Also, I would like to note I did not micron filter the methylone when I IM'd it, but when you're taking as large of a risk as injecting RC's of unknown purity, micron filtering would be the smartest thing you could do. Especially for IM, where an infection/abcess is much more likely.