The only way I could get them cubes to work was to wet them and then leave them on a few layers of paper towels to get the moisture back out.I use the little cubes to clone and start seeds. Never had issues. The trick is to let them sit in the seed starting tray with a heat mat or in the sun to get rid of some of the moisture. I have a little thing they sit in at the bottom of the tray and I then poor water into the tray just below where the cubes are sitting. This ensure they stay moist and not wet. Pretty much 100 percent success with seeds unless they are super old and a solid 90 percent I would say cloning which is better than my clone machines and easier to transfer.
Now that I know grodan doesn't need to be pre soaked I would just dunk them up to halfway and leave the top dry completely.
I feel like root riot cubes are easier tho and need no fuckery so I use them but it's good to see you got them to work with a heat mat. Ive always worried I'd get root rot or something so I stay away from them lol