It's been a while and I forget the details of exactly what flow or set of steps led to me impotently clicking on things that were unresponsive because a Glance popup was on. I remember being annoyed by it relatively frequently. The memory I have of it was that Glance was cool to have going into it, but almost always frustrating to have to close again.

To be clear, I have no horse in this race. I encourage people to try Zen and Firefox and pick either of them over any of the Chromium hordes. I'm just explaining why I went into Zen, used it primarily for a while, side-by-side with Firefox when vertical tabs came in and then phased it out because FF was a better fit for me. There is no us vs them here at all.