I leave the mount on the screen. Holds well.
The satnav is held onto the holder by a super magnet. Connections are part of the fitting so simple to disconnect.
I don' like the phone ones - can't surf the web at the same time.
I have one built into the head unit but, whilst good, it just isn't as adaptable as the portable ones - i use it for a journey overview.
Like all toys, i suppose i all depends on how much you'll use it as to its value.
I cover North of Scotland to 6 finger bumpkin territory (Cornwall), so for me, it pays for itself.