I believe the normal H3 sponge is 2.2mm and H3Neo sponge is 2.1mm so for those who want to boost and participate in tournaments that have racket control testing it’s best to go with H3Neo that way less likelihood of failing racket test if overboost.
Nope, there are both neo and non-neo versions of H3 with 2.1, 2.15 and 2.2 thicknesses.
However, H3 NEO produced after some date are not tacky anymore, the sponge is much more lively and requires less boosting.
Non neo in my experience is still much more tacky, the sponge is completely dead without boosting.
It seems that no one really knows the reason, but speculating that DHS changed the formula to suit better for 40+ plastic balls.
Some like newer non-tacky H3 more than old one, for some it's the other way around...I think newer NEO version is suitable for most players.
However, my w968 completely sucks balls with the new H3 and excels with tacky H3 or 729 Battle II, which is also tacky, but less powerful 🤷♂️
edit: addition. H3 NEO is fine on my more stiff blades, even on 5 ply Neottec Voodoo Classic. It produces less spin than tacky H3 over the table, but the sponge is faster in general.