So this isn't a spoiler cause its the same as in OB sign, 50% magicka absorb, -50% magicka regen, +50 magicka.
Well since magicka absorb is godly, +50 magicka is nice, and this sign along with alteration perks can theoretically make you immune to magicka and actually make you WANT to be hit by spells, a very attractive stone.

We know that all magicka regen effects don't work in combat and it seems to regen at a static rate, maybe this needs to be tested with extreme amounts of regen. But assuming that the penalty only effects out of combat regen, then I couldn't care less.

Also it would be interesting to see how penalties apply to calculations. Does 50% penalty offset 50% bonus in an additive way, or does the 50% penalty offset a 100% bonus in a multiplicable way.