Firstly I really like the egg-timer thing, I think I might adopt some version of that.
Secondly having a communication tool doesn't mean there will be communication. After all, you should prefer that your egg timer never gets used, right?
If the egg timer keeps getting flipped, your game table is failing. Not necessarily terminally so, but the egg timer doesn't directly fix the root cause, it isn't intended to.
(That said, I'm happy to accept that it might - if the same guy keeps getting the egg timer flipped on him, hopefully he will start to learn to sharpen his play.)
I'd also dispute that the X-card doesn't mean that you can't talk like adults. In fact I would argue the reverse. "I am starting to have an issue, I'd like you to listen to me". I think it immediately focuses the conversation, gives a start point for an adult conversation, distinguishes it from a regular whine. Now the GM can decide that the player should suck it up or leave, the player may make that decision for himself.
I've thinking back at all the tables where there have been bad experiences (not necessarily my own) - the egg timer would have certainly some of mitigated those, some version of an X-card might well have mitigated others. In many cases, no system would have mitigated the issue which was fundamentally interpersonal.
There is merit to your points here. I thought about the egg timer as something analogous to the X-card that we use. On the surface, it might sound as if I'm being terribly inconsistent with my positions here. And maybe I am, somewhat. I went ahead and used it anyway, because I'm not trying to win an argument but to explain where I'm coming from.
In practice, we don't flip the egg timer much. That's the other thing that prompted the comparison, since you and others had said it didn't get used much in your games. Here are the difference, in my opinion, in the timer and the X-card:
1. It's not linked to a specific behavior or possible problem. I suppose that could make it a bigger potential issue with a jerk player, not less, as there is more room to abuse it on those grounds. That doesn't particularly bother me, because tossing the jerks sooner rather than later is the end result. Maybe in a game with strangers, that's a relative negative for the timer, positive for the card. I don't know.
2. In practice, though it doesn't get used much overall, it gets used in spurts. That is, we only started using it because there were particular issues that kept occurring, but trying to stop the game to fix them was difficult, because it would interrupt the flow of the scenes. We wanted a way to signal, more or less, "I don't have a problem with what you are doing, but it has run on too long, and I'm ready to do something else." It's not a veto, hard, soft, or otherwise, or in anyway trying to draw firm line. Once it gets flipped a couple of times over a particular issue, we don't tend to need it again, because there is something psychological about the 3 minutes of sand running through the timer that flips a switch in peoples' heads. After that, one person merely glancing at the timer can be enough to get the whole table to unconsciously get on with the scene.
3. The flip side of the veto issue, the timer has two different ways to acknowledge. Finish the scene or explain why you need more time to the rest of the group. Because of the options, the timer itself exerts no control over the scene at all. Compared to the X-card, I'd still have objections on the "gaming isn't therapy" grounds to using one, but it would be immensely improved as a communication tool with even one more state. Something like, "touch the X-card to indicate that you are uncomfortable with what is happening but not ready to bail yet and/or would like it to end soon or at least back off a little," versus "pick up the X-card to say that this suddenly went way over the line, and you need it to stop right now." Only the latter is a hard veto and off limits to discussion.