Not sure I get the gyst of this, Tax. It seems to me that the OP (DGV) asked for opinions on isolation systems for turntables which is pretty well what members have responded to.
That is exactly what I believe we were/are trying to do. Share experiences of isolation techniques and where data is available or published by respected manufacturers this should be raised for all to digest.
Turntables come in many shapes and sizes as we all know. Suspended, non-suspended are two broad categories most of us have either direct experience with as owners or have friends with one or the other.
Some of us have audio rooms on upper floors or have to contend with older houses in need of improved floor support. So wall mounts are popular to avoid the problems of footfall bounce. How many of us have to tiptoe around our tables when they are playing to avoid needle jumps?
So the suspended tables get a few points for attempting to address these common domestic installation issues. Some like the SOTA, Avid, Basis or the SME do a pretty amazing job of isolation and do so right out of the box.
For non-suspended tables the floor problem becomes an issue. So the use of slabs of concrete/metal/wood with air bladders in between do provide a relatively low cost way of creating a compliant interface between the table and it's mounting surface.
Rubber inner tubes can be deflated to create a super "spongy" interface (low natural frequency). Occassional pressure adjustments can be an annoyance depending on your point of view. (Cost vs Performance).
Suspended "bungee" or "hockey strap" systems also work a treat but tend not to have a good WAF in the looks department. However they can be made to support a heavy table and can be loaded to have a very low natural frequency (1-2hz) both vertical and horizontal (pendulum). They have limited adjustment via mass loading or subtraction. Again low cost.
Once you start looking at commercial alternatives such as Vibraplanes, Negative Stiffness mechanisms, Active Piezo or Voice coil solutions then you can get access to manufacturers published specifications.
As these sources are often focused on the scientific or engineering community you can rely on published specifications to be very accurate. Active systems are proven solutions used in many laboratories around the world. They work well in some pretty impressive sites. So do the Passive alternatives.
So when faced with a choice of isolation solution it would be good to look at the problem at a high level to decide which is best for you.
For example what is the total weight of your turntable?
Compare this to the total weight of your stand that you intend to place the turntable onto.
If you place your isolation system between these two items one should consider if the turntable (i.e a high mass non suspended table) is heavier than the stand it sits on.
If for example you use an active correction system and it "pushes and shoves" your table in its correction mode and the stand you have seated the table on is lighter in weight - then the stand will move before the table and there will be an overshoot and lag occuring.
To address this you need to stiffen the stand (preferably infinite stiffness) so that it does not move when the active system is "pushing and shoving" and performing the correction cycle to external vibration.
On wooden floors the stand will rock the floor again leading to lag and overshoot.
So for the active system to be allowed to work at its optimum one should consider a high mass stand well exceeding the weight of the table. That way the isolator will be given the best environment to deliver the published attenuation.
An active system based around a feedback loop can only deal with feedback signals that are so large. When these are exceeded the feedback loop can go into a positive feedback state and ring. This ring is vibration. Active systems typically have a dynamic range (maximum displacement capabilities) on the order of a few thousandths of an inch.
Passive systems such as the MinusK can deal with vibrations that are MUCH larger. This is why they are often chosen for isolating footfall problems on upper floors.
GFunk pointed out springs will exhibit some non-linear behaviour. Have a look inside the mechanism and see if there are springs used. All systems with springs will exhibit some form of non-linear behaviour in action. Even soem Active solutions use springs inside to assist the voice coil actuators support the payload.
For the audiophile to hear these "non-linearities" would be difficult as the isolators bring overwhelming benefits. Yes Active systems will actually be better than no isolation at all. So will Passive systems.
Compare the published isolation specifications, and work out the maximum displacements you will experience on your floor installation. Even concrete floors still transmit vibration - just ask any laser interferometer or LIGO researcher who probably has war stories of truck traffic 2 kilometers away disturbing sensitive observation systems.
So if your budget is able to expand to include commercial isolation solutions for your non-suspended table then the sonic improvements far outweigh the negatives (cost, looks, mounting concerns etc).
Suspended tables using additional suspension systems are a whole nother discussion.
Happy to discuss
"There are three types of people in this world, those who can count and those who can't" - Rod Quantock