Lets open it up and see what we get
Considering that you'll get one of these cards in about one in every four boxes, this means that the Invocations add about $11 in value to the expected value of a box of Amonkhet , bringing the total box EV up from $77 to $88, which is approximately $10 a box less than either set from Kaladesh block and way less than high-EV sets like Khans of Tarkir or Battle for Zendikar
It turns out that there are more than a few creatures that get a lot better when you turn them into artifacts and give them a mana ability, especially if you want to give yourself a repetitive stress injury in your wrist by tapping and untapping Horseshoe Crab, Simic Ragworm, Soliton, or Morphling until they kick you out of the LGS
Given that, there are two schools of thought when it comes to preparing for a tournament
It comes in with X counters and hits that many nonland permanents until it leaves the battlefield itself
Instead of merely, making the creature sacrifice itself to counter a spell, we used the same trick we used on Ravenous Baloth and Wall of Mulch