Shulgin seemed rather to like the PMA, although warned of deaths, never tasted either PMA, PMMA or the beta-C=O derivatives myself, meph/methedrone both look plain fucking ugly as shit, if you choose to take it, work your way up from I would say, no more than 10mg, after a preliminary allergy test.
The butanamines appear by weight to be weaker than the corresponding phenisopropylamine (not speaking specifically for the para-OCH3), and as there is a significant chance that much of the toxicity of mephedrone and its nastier little friend methedrone is in a large part coming from its metabolic degredation to the corresponding ephedrine, and in the case of the methoxy compound, aromatic ether cleavage to the 4-OH ephedrine which appear to be quite potent vasoconstrictors (amongst possible other, less pleasant effects still, such as those reports of persistent circulatory and heart issues)
PMA has a very steep dose-response curve, not so sure about the secondary amine (PMMA) in comparison, but the beta-keto-2-aminobutane is going to be less potent by weight than either PMA or PMMA, or mephedrone/methedrone, and I believe thus, given the strong reinforcing properties of the latter two and how likely this is to be taken in repeated doses, compulsively amongst many users, it will display a strong increase in potential for toxic responses or deaths, due to the corresponding increase in levels of the ephedrine-like metabolites.
IIRC, although again I have never tried it, buphedrone and butylone have more adrenergic effects than the amphetamine counterpart also, so doubly nasty if this is so.