I’ve been using one for years in my racing rig (may add more in the future) and I’ll have to say it adds substantial immersion. Haven’t tried it with MSFS yet but I’m not convinced about it.
It’s one thing to have your entire system (bucket chair, metal frame, wheel, gears etc) vibrate variably for 20-30 minutes of intense racing, especially when you’re going over curbs and you ask for that vibration feedback because it helps you find the limits of the car and perform better. And it’s a different thing to be for a couple of hours in a Cessna with a steady vibration which certainly adds to immersion but I’m not sure about the rest.
This means that it’d be a fantastic idea to add buttkickers to your MSFS configuration, but personally I wouldn’t spend a fortune in them. Just the basic stuff.