I personally prefur th raven but with anything like that just don't have it on or around your bank cards it will erase the data and make them not work and useless.
I've done this...... Twice
it´s very powerful...that means that if you are not careful with this you may stick to anything made of iron, even if it´s inside your pocket, so you just have to be careful.
Good point about the M5 being a very strong magnet. But with something so heavy tucked inside your clothes, Im sure you must be able to remember whats around you at the time of performance, After all there is sooooo much you can do with this device.
I used to live in Toronto,went to a subway station, I had my raven on ready to go, went to pay walked through the turnstile, looked back and my arm was stuck lol i assume the same kinda thing can happen with the m5