They are 2mm deep, which is a bit of a nub on a naked phone, but it sticks out no further than my phone case, so i dont notice it.
It is a rare earth magnet, so will attract keys, coins, metal filings, however the brass electrical connectors are 0.25mm recessed into the body, ive noticed no issue with shorting across the contacts, and ive never had “bad connection” issue with the cable either
similarly the cable end is magnetic, but i tend to use that to tack it onto my bedside lamp so i know where it is in the dark
It has a very bright green LED on the cable end, but i put some tape over the ones i use in the bedroom.
Connector works both ways up too, which is handy, and i believe the same cables can be used across all the connectors (USBC, lighting and MicroUSB)