I can’t speak for the others, but at Manifestly, we’re targeting SMB and most of our customers are teams in the 3–50 people range. We have some large organizations using our service, but not the whole organization, just a team within it.
As for the portability of the process docs. We provide an easy way to export your checklist templates and will work with anyone to export in specific formats to meet their needs. We don’t like walled gardens ourselves and will do what it takes to provide portability if an organization leaves our service.
You can see our features list here if interested.