Very tough question.
Immortal soldiers means the cosnsequence of war is diminished, which may make it more appealing and shift the balance of power in unpredictable ways.
Selling it (legally) would likely be a regulatory nightmare.
Sharing it with your family and friends is nice, but what about their family and friends who don't get it?
Keeping it a secret is a heavy burden to bear, especially if you have children.
If it was made widely available to anyone, the earth and humanity would, putting it mildly, have an "adjustment" period, but cultures and societies would have to adapt eventually.