On their own, yes. The ones I can make only last a few seconds, so I've never worried about closing them behind me.

Not a lot. From other Travelers, mostly that it's got something to do with the Trumps, although... I'm not sure I agree. They meddle in things, but this would be showing their hand a lot more than they usually do. And you'd think they wouldn't want random people wandering into Liminal Space.

[What with the problems they've had in the recent past]

I don't know what the natives think of all of it, though, or even if they have a consensus opinion.