I personally think it is quite impossible to assess if the volume control is really risky before trying it. And let us give Calyx some credit on this.
But Calyx
already had the slider flush, and the buttons proud.
It's not like anyone is asking them for something they didn't already choose, previously.
This has been discussed quite a lot, during this thread:
http://www.head-fi.org/t/687944/999-calyx-m-with-dxd-dsd-64gb-sd-sd-storage/690#post_10235378
http://www.head-fi.org/t/687944/999-calyx-m-with-dxd-dsd-64gb-sd-sd-storage/990#post_10263449
http://www.head-fi.org/t/687944/999-calyx-m-with-dxd-dsd-64gb-sd-sd-storage/1125#post_10276014
Buttons were proud at this stage
(good for [REW][Play/Pause][FFW] buttons, but bad for volume slider, which was previously flush):
http://www.head-fi.org/t/687944/999-calyx-m-with-dxd-dsd-64gb-sd-sd-storage/1170#post_10279738
and
now, volume control
even more proud, and buttons made flush, for some bizarre reason:
http://www.head-fi.org/t/687944/999-calyx-m-with-dxd-dsd-64gb-sd-sd-storage/1275#post_10298475
(...and in many more places, but no point in posting them all)
NW-ZX1 may not be the very best DAP on the planet, but it
is something of a masterclass in terms of the ergonomics of its control buttons.
Calyx did, at least, keep all the buttons on one side of the chassis, so as to avoid accidentally pressing a button simultaneously on the other side of the chassis to the button intended.
But making the buttons
flush, at the last moment, is barely any more useful than touchscreen-only controls, other than that they don't require a screen-unlock manoeuvre.
As for the silly proud volume slider, I really wonder what EU safety regulators will make of it...