Each ability can only be chosen once each turn but pair it with the likes of Escape Protocol to blink it and you can activate abilities as much as you're able to
For Value If you want value for your money, then Mystic Intellect is your pick
Similar to the other Forces from the MH1 cycle it can be cast without tapping any mana, making it automatically very interesting in the fast Modern environment
While it doesnt exile permanents, unlike its Battle for Zendikar counterpart Ulamog, the Ceaseless Hunger, destroying a permanent is still noteworthy, and coming with Annihilator 4 allows you to put one of your Commander opponents into absolute ruin
Although only costing two mana is nice, getting only one +1/+1 doesn't do a whole lot
If you're starting without any Zombies, it takes a very long time before you start amassing a large battlefield of Zombie tokens, and at that point, you likely could have built enough of an army of regular creatures