I got my Isis puzzle open, and having now had a chance to thoroughly inspect the mechanism I discovered two interesting things: the solution on YouTube doesn't actually work, at least not on my puzzle, and the Isis really is every bit as bad a puzzle as I thought.
Warning: spoilers follow.
The internal mechanism of the Isis would make Rube Goldberg proud. The sphere consists of two hemispheres that are screwed together with an inverse thread so you have to turn the halves clockwise in order to open the Isis. The two halves are normally locked with a locking plate that is held in position by a spring. The button on the top of the puzzle is used to push the locking plate unto the unlocked position so that the two halves can be unscrewed. There are two obstacles to moving the locking plate: there are two ball bearings that normally block the movement of the plate. These need to be maneuvered into indentations in the locking plate in order to get them out of the way. And the plunger attached to the button is not quite long enough to push the locking plate into the unlocked position. In order to extend the reach of the plunger, a third ball bearing needs to be maneuvered into yet another indentation directly beneath the plunger.
It is this third ball bearing that causes all the trouble. It is normally stuck to a magnet in the upper half of the sphere, and dislodging it requires striking the sphere on a hard surface with considerable force. It turns out that the problem I was having was that I was just not whacking it hard enough. In order to make it work I had to take the sphere into my garage and hit it against a wooden workbench with about the same amount of force as it would take to drive a nail into a 2 by 4. And the worst part is that there is no way to tell if you've successfully dislodged the ball bearing from the magnet. You have to fly blind.
Once the ball bearing has been dislodged from the magnet, it has to be maneuvered through a maze that has been machined into the locking plate. This is a part of the mechanism that the YouTube video does not reveal because it is hidden behind a steel cover on the locking plate that has to be removed with a screwdriver. Maneuvering the ball bearing through this maze is the step that is supposed to be accomplished by moving the puzzle in circles a few times, but it doesn't work. The maze is too convoluted. It took me quite a while to devise a series of moves that would reliably move the ball bearing through the maze, and that was with the cover off! The resulting sequence is so subtle and convoluted that I can't even describe it in words. I would have to make a video of my own to show how it's done. I'll only do this is someone asks. It is quite possible that different Ises have different maze configurations, so my sequence may not even work on other puzzles.
Once through the maze, the ball bearing ends up in the center of the locking plate. It is not until you get to this point that you get your first bit of feedback that you've made any progress at all: when you press the button now it no longer goes down as far as it did before (because the ball bearing is in the way).
The encrypted clues call this the "halfway stage", but once you've gotten to this point the rest of the procedure is a cakewalk by comparison. All that remains is to maneuver the two other ball bearings into their indentations, which is relatively easy because they run in circular tracks. All you have to do is turn the puzzle upside down and gently "wobble" the puzzle until you can no longer hear the sound of the bearings moving around. Of course, you have to be careful not to dislodge the first bearing while you do this, which is accomplished by exerting *gentle* pressure on the plunger to hold the bearing in place. Once the two bearings are in their indentations, a firm press on the plunger will move the locking plate into the unlocked position. It will snap into place. At this point you can let go of the plunger and unscrew the two halves of the puzzle to obtain your prize, which is...
Nothing! There is, as the YouTube video shows, absolutely nothing inside the sphere besides the mechanism. And, as a final insult, it is trivially easy to lose the crucial third ball bearing. It will just fall out if you turn the puzzle the wrong way. If you should happen to be so unfortunate as to not notice that the ball bearing has fallen out and reassemble your puzzle without it, you will likely never be able to open it again. No wonder they don't accept returns once the seal is broken.