I've tried this on both my end game mage as well as my level 10 twink mage, and here is my analysis:

1) At end game it does little in a 1 on 1 battle. As was mentioned by Shiny, since you can be one-shot by a rogue, healing yourself is not going to help you in such a battle. Plus, even without the regrowth upgrade I was able to fully heal myself from about 20% health.

Where this would be useful is in a clash where the sorcerer is now able to fully heal a warrior with 7500+ health. I always thought sorcerers should have the best heal skill, and always thought it was strange that warriors did. In Pocket Legends, mages had the best heal. So now maybe it is so, although the warrior heal skill still provides the very useful shield for everyone.

Another thing I noticed is in PvE I can cast heal and run into a mob attacking, and when I take damage the health regen is still going (much like when a warrior heals) and so I end up healing myself.

2) At level 10 this is a game changer for mages. I'm not sure about other popular PvP levels, but at level 10 sorcerers were always quite inferior to the other classes. They were basically only useful in clashes to cast their curse, but in a 1 on 1 battle against a warrior or rogue they were useless. Now this all changes. Before this upgrade I was only able to fully heal my sorcerer from about 60% health, and since my sorcerer has 8 para gems, I'm guessing most level 10 sorcerers could only heal from about 75% health. But now with the increased health regen, I can fully heal from as low as 10% health. This is a major game changer. While I haven't tested it out that much yet, it appears that sorcerers will now be able to compete much better at lower levels.