I have one of these:
https://www.amazon.de/-/en/dp/B01HY74VVA
I don't think they are made any more.
They are quite strong (and stable & large due to the bottom plate), but also not quiet (I share a place with colleagues, who are tolerant of my ways, but prefer not to involve them directly 😉 lol) - you can hear it outside of the the room you are in well.
I did remove the speed dial from the main unit and have it attached via a cable & extension box so I can control the speed without reaching back (which is next to impossible, lol). I also added a bolt on adaptor plate so it can be used with any suction cup dildo (the one it comes with has a nice shape, but is really stiff & hard).
It is fun sometimes, but such machines are not very interactive, you can control the speed but otherwise they just "have a go at you" so to speak. Interactive IRL partners are a lot more fun....
I unfortunately can't find her original page, but someone reposted one of her videos (to avoid dead links as attachment below). This has always fascinated me, it is a very ingenious non motorized DIY f-machine made by mounting a dildo on a gliding ottoman foot stool [they have counter balance springs to cause them to return to a center position] and a mop handle for controlling the swinging speed/strength... lightly with your finger tips... Not so much of an option here in Europe, but on the other side of the pond most people's grandparents probably have one kicking about....
gliding-ottoman.mp4 (Size: 49.7 MB / Downloads: 49)
Similar principle to the "monkey rockers" ... but they are *really* expensive & have read not optimal for around back... has anyone here ever tried one of these?
https://www.amazon.de/-/en/dp/B0BWJ2YRBN