The problem: the magnet is too weak to produce a mechanically flawless and even halfway stable connection. The idea is not bad, but the implementation - probably because of the construction is unsatisfactory.
And I am not talking about calls with cable connected; that works eh not because it falls at the latest. But already moving the phone while lying on a table leads mostly to the fact that the cable loses connection. And even with a stationary phone is a positive link bit fiddly.
Conclusion: Stay away, instead buy a dock or a normal microUSB cable.
