I think the issue is, really effective against what? For example, a Linn, although spring-mounted, is terrible with footfalls, while a Basis, also spring mounted, is much better. There are many theories as to how to design a tt. Some say that spring-mounted tables are always in a state of oscillation and that a heavy plinth is the way to go. So the short answer is - I don't think you can generalize about these things. Each table has to be judged for its own merits and you shouldn't be shopping for a tt based on whether it is suspended or not. There are just too many factors that contribute to the sound.