Yesterday I had a 1st training with the H3N. The setup is 199g, with R9 H40,5 it was 192g, but it's not so that the H3N is 7g heavier, it's perhaps 3-4g heavier, because R9 was re-glued 2 times, and thus stretched and cut and thus made lighter. Also I applied glue generously for the H3N. But it does seem it is a bit heavier, and recently someone asked for lighter H3-like rubber, to which I replied it will be hard - now I correct myself, Rxton 9 is very H3-like and a bit lighter.
Regarding playing, first I don't mind the weight. Due to the new tackiness, the bounce is less on small hits in compare to the used R9, so I thought that a break-in period (1 or 2 trainings) will be needed. But it was not so, I could immediately adapt to H3, I didn't feel I need corrections. The rubbers are indeed close from the type of response. I enjoy the H3 H41 very much, especially on stronger hits it will not let you down, it will always make nice arc. The top-sheet is tiny bit different from R9, perhaps the H3 top-sheet is tiny bit stronger and R9 is tiny bit more elastic. But for me, they are closer to each other, than the H3's distance to D09C top-sheet.
H3 and R9 are for me the best dense-sponge rubbers. I'll play the 2nd half of the season with H3, and then I have some older rubbers, both FH and BH which I need to spend before I buy some new rubbers. That means, while I am interested in rubbers like J1 or Nuzn 55 (and the experiences people write here), I won't buy those in 2026. --no-more-ej
EDIT: Regarding the adapting, I had a hit with "729 Faster" rubber, which is also a tacky and dense-sponge rubber, and here I couldn't land consecutive FH top-spins. There the sponge response really is more different. I would adapt, but not immediately.