I’m using my DIY buttkicker (in stereo LOL) on my DIY motion rig and was using it before the motion rig too. I’m driving it with SimShaker for Aviators + Sound Module (must have for event feedback, like gear, flaps, groudn roll, touchdown etc.), and also mixing in some low end from the MSFS original sound.
It adds a lot to the experience. Not sure if it’s as huge as the motion rig in terms of increasing immersion, but it is comparable. When I added transducers to static seat I was blown away by the difference. Motion blew me away even more, so you should definitely have both. They add to each other for a total immersion. When I forget to switch on transducers or they lose connection after MSFS CTD - it really feels like I’m missing something, even with motion.