The guillotine placeable was used recently in Cordor during a player event, but the guards ended up using a sword (and quite a few chops) to simulate it's use.
You also have the body to get rid of, which in many cases you don't wish to 'reward' their RP with bashing.
Suggestion is to have a few fixed (1) guillotines that the intended prisoner can use to be teleported (IC slain) to elsewhere (2).
(1) Fixed to prevent carrying guillotines around for personal transportation use in emergencies! Potentially barrier its use behind settlement machinery.
(2) Fugue springs to mind, but could even go to the relevant alignment plane or respawn location for free, if a god roll succeeds. Main purpose is a non punitive IC removal of the prisoner from the scene playing out.