Hi chadhump,
Hopefully you’ve had the chance to read the tutorial post (the link is at the top right of the page) which has all the basic information, steps, and guidelines that can help you make the best possible choices … and avoid the worst ones.
Outside of testing a mattress for PPP (using the testing guidelines) … a mattress is only as good as the quality of its construction and the materials inside it so it’s not really possible to make any meaningful comments about a mattress unless you can find out the specifics of the materials and components inside it (the details you would need are in post #4 here).
Without this information you would be making a completely blind purchase and there would be no way to identify any weak links in the mattress or to make meaningful comparisons with other mattresses.
In the case of the King Koil G6 you can see most of the specs and my comments in post #2 here.
It’s certainly not a mattress I would consider.
Phoenix