I have read quite a few more trainwreck reports about MXP than diphenidine. Also there was a report of a guy who was all fucked up on MXP murdering his mom, with associated news article posted. Having never tried either, my impression is that you need to be even more careful with this one than diphenidine.
I would think they both have the same potential although I have not researched diphenidine myself. I keep seeing diphenidine as being the most amnesiac one based on the threads and reports I have read but as I have said, not versed in both substances. I feel like it is pretty safe to say that both compounds need to keep the dosage under a certain dosage level. Once this 'ceiling' is reached, going over only ends up with the person in a bad place.
The murder comment is no different than if one were to drink too much or take too much benadryl or perhaps ambien, people who become intoxicated do things they would have never dreamed of doing while sober. I don't want to say it wasn't MXP's fault but yeah, it wasn't MXP's fault for the murder, it was caused by unsafe research practices to put it a bit too bluntly. Caffeine can make certain people manic, certain manic people can kill people, caffeine by itself can kill people but it is still not the fault of caffeine, it is the fault of the person who took too much.
Sorry to veer it off-topic, this compound should be researched only by those who are diligent enough to take care with titrating things slowly.