I've used a Vacuflo 566Q and a VacuMaid S2600 that both had the soft start feature (coincidentally they both had the same motors). I've also had some Simplicity units made by the same company as CycloVac that used the soft start feature as well when I was working at a vacuum shop. Personally, I'm not a fan of it. It makes sense from a technical point of view but I prefer having a unit that starts up immediately.
Going back to the original question of this thread, I've got several videos on my channel with central vac videos. Some of which are mine. Right now I use a Beam 287S in my home. I also have a Eureka The Boss over in my storage shed. And in my collection I have a DrainVac Little Giant. I used to have a MD SilentMaster (believe it's a S2), left that behind when the place got sold. My all time favorite central vac ever would be the VacuMaid P-125 that my grandfather has. When I move, it's going to have a central vac since I can't live in a place without one. Would love to get another MD but open for other options like Vacuflo.