spring loaded platform non-suspended turntable

Crubio, I'm not an engineer but I'll suggest you need to consider three conditions. One is acoustic vibration from your listening room environment. For example, where is your turntable placed relative to room node build-ups? Hint: avoid placement in any corner, bass range build-up is greatest in those.

Next are the mechanical vibrations generated by the table itself. Slate has a good reputation for absorbing (draining) low frequency vibrations so that, along with your 100 pound mass, should do well in minimizing this problem.

Last are the external mechanical vibrations which can affect your turntable/arm/cartridge performance. This will vary from set up to set up. Do you live near a street/highway with heavy traffic? What is the construction of your floor? What kind of stand is your table mounted on? Is it mounted on a shelf attached to a load-bearing wall?

Depending on your conditions, adding any sort of suspension may or may not improve your listening. If you could find a modestly priced suspension system (inflated tube or bladder) to try for comparison against what I assume is your current non-suspended mounting, that should indicate if it would be worthwhile to then explore suspension options.

Sorry, there is no simple answer to your question.

Since my place is old and I live on the second floor, isolation is a must. I'm certainly getting feedback through the floor, no music above 90db. I bought a stand from a research equiptment re-seller, it's made by Newport, not audio jewelry, but not horribly ugly either. I'm in No-Cal so such business are available in my vicinity. It's built to handle very heavy things. I'm going to go for the Minus K since it's free from the need of a compressor, and is made in the US. We will see.

In MY experience, non suspended turntables need a solid foundation to the center of the earth... Spring aids, ruin the sound.

I put my Rockport Capella II on a pneumatic anti-vibration table, similar to that under the Sirius III, and experienced considerable improvement in term of background blackness with no negative effect that I could hear.

My friend put his Technics SP10 MK2 on a Minus K and got similar improvement in background blackness, but I was not familiar with the system so couldn't tell whether there was any negative effect.

However, the Minus K is not self leveling, so if the CG of your TT is not exactly at the centre of the platform you need to add some weight and move it around the platform to level it.

Let's see, if you have an unsuspended turntable on a solid unsuspended base, the structureborne vibration can get right up into the turntable platter, the tonearm and the cartridge. That being the case, I would probably opt for some kind of vibration isolation system.