So far as I can tell this is safe and works (ymmv)

This code (run with root privileges):

instantly puts the n810 into standby sleep mode
(or whatever it's called)

A brief push of the power button wakes it up again
(you get an interesting dialogue when it wakes).

Ah ... I see that dialogue comes up when the tablet
is awake and you briefly push the power button ...

In KDE Konsole shell on my N810, this gets me
/bin/sh: cannot create /sys/power/state: Permission denied

It doesn't work. The device gets rebooted by the watchdog after about 1 minute (you did not try it that long, did you?).
A "suspend.sh" script that solves this problem has been posted somewhere on this forum or mailing-list.

if i remember well the watchdog can be disabled using the flasher.

yeah, not so good. I find on mine it shuts down after a minute or
so. It is also flaky - sometimes the keyboard does not wake
up. Cannot find any suspend script here. Do you have a link
handy? Thanks.