I wouldnt be without mine and feel it should be in line of sight but thats my opinion only
other option would be to fit it behind the vent slats , camoflage styleee, so you can still read it but its less obvious?
(in fact I might try this myself
)
lots of options, in the tray is fine , maybe even on a longer lead so you can just 'bring it out' when you want to ?
your options are endless