I too used the original Herbie’s dampers for many years. I now use the double o-rings that Conrad Johnson provides.
If you decide to use o-rings, be sure they are designed to be used with tubes. I have heard of people buying basic one’s from a hardware store, and having them melt.
It is one of those low cost tweaks that at worst do nothing, and do no harm. I believe they help, although I have never did any serious comparisons.
I would stay away from the shields, or those things with the springs on them. As I too question whether they do lower heat. I think the shields may have been used in the past to lower noise, or avoid interference. In the past, tubes were used in some environments, that we would not do now. For example car radios. My 1955 Chevy had tubes in the head unit, and an amp behind the speaker in the dashboard. Imagine the beating those tubes took.