With small tanks, this stuff WILL make the tank wabble. I find that with large tanks, this is not necessary either. Think about it... say a camping mat, or even that floor thing. 190g is close to 2 tons when full, therefore the mat will just squish to a fraction of the thickness it was and get very dense...therefore any imperfections will just move the material upwards and you end up with an uneven surface anyways.
I built all my stands, and don't use any of those. The wood piece under the tank has to be perfect...lots of sanding and checking, but it works wonders. I'd say you are better off making sure the top is nice and smooth, than to try and pad it with something.
My 2 cents...