*snip*
3. I'm not sure about the anti-synergy with SoD and stone skin. Max HP does not affect this card. Only your current HP and number of cards in hand will determine whether you gain 10 HP or not.
*snip*
This is mainly an issue for beginners and grinding based decks. Particularly EM
The payout you get after a game ends is based on your %HP remaining. In order to get an EM, that has to be 100% ... So this card will be much less useful with each SoD used, since at best, you only get healing if you have 80 HP or less. If you only need to stay healed to 100 HP, then this is fine since sanc, luciferin, or Holy light takes care of the rest.
Once you use 1 SoD, however, you now go from a 20 point deficit to 36 or 44 point deficit. Thats a good deal more difficult to make up in one round.
So, yes, max HP does not affect this card, but it will affect the percentage of winnings a player gets at the end of a game, and it will especially affect their EM chances.