I'm not super fond of the art for the dragonorb. It looks more-knick-knack and less crystal-ball.
I understand your perspective, and of course the whole point of artifacts like this is so that you can connect the PCs to a larger story, in the way you want. I would probably run it similarly; the player might get visions offering clues to what Vecna wants accomplished.
I think as a player I would enjoy the dynamic created by the flat probability, though. How can I know whether my actions are in line with Vecna's desires? Maybe I think I'm spreading evil but really I'm interfering with one of his more subtle plots. And from a gamist perspective, every time I use the Eye I risk my life. Am I never going to use it? Not likely. But every time the chips are down, and I'm tempted to use the Eye, the game has created an edge-of-the-seat moment. It's not everyone's cup of tea, obviously, but it is in line with a "let the dice fall where they may" attitude toward gaming, where getting a PC to high level takes luck as well as skill, and is not guaranteed. That's the kind of game I prefer as a player.
Of course, as a player I would never attune the Eye. But hey, what if some evil cultists kidnapped my PC and implanted it by force? Then I'm stuck with it.
As I DM, however, I would never introduce the Eye without also giving the players a way to learn that the 5% risk exists.
First and foremost I don't go into every thread complaining about the same topic. I make a critique or observation that is negative about something I don't like, but the overall game is good or I would not run it and play it.
The point is to be honest, some things are not perfect. If all people do is hear positive feedback they won't know what they did wrong. It seems sometimes any criticism is seen as pure unthinking hatred, when it is exactly the opposite. If I didn't enjoy the game I wouldn't care.
* the new mechanics are crappy. It shows most with the artifacts : the removal of the clever building up frameworks introduced with 4e is a terrible shame. Where are skill challenges, disease tracks and artifact tracks when you most need them ? Neither as a player nor a DM would I seriously consider using/introducing this Eye of Vecna : flat 5% of losing a PC forever to use Clairvoyance is silly. It tells the story of a DMG written on a budget, leaving large gaps in the DM toolbox. Fortunately for WotC, I like the rest of 5e so much that I am looking forward to the Unearthed Arcana which is inevitably coming to fill the holes !