The first issue with that is periodic limb movements (or PLMs) by definition can actually range from subtle movements almost like muscle spasms to large limb movements, so constraints would be limited in efficacy for that purpose specifically. This would also surely negatively affect any insomnia, sucks enough waking up at 2am involuntary when I'm not in restraints

That said, my father has a sleep movement disorder as well- but his is more extreme and called REM Behavior Disorder. Basically means he physically acts out his nightmares on a regular basis. His neurologist has been trying to convince him to put barriers on the side of his bed so he doesn't fall out and injure himself but he's been hesitant. sucks getting older.

These don't actually prevent moving. Restraints simply mean the movement won't be large. Great solution to prevent damage if you hit things in your sleep or, say, you have had a stroke and can't control one arm. It just doesn't actually prevent the movement or the signals that make them (muscles will still get the signal to move).