I actually have one a bit similar to the pink one. It actually has buckles that go around you. I couldn't find it on Amazon (I won it in a pet contest)
I did try it on and put my smallest Chi (Buddy Bear a 4 pounder) He actually seemed okay in it. We didn't go any where just at home but I personally didn't like it, felt weird. And haven't used it since.
I personally don't like the idea of a dog just hanging out in one of those. (Maybe one day I'll change my mind) But I do understand to some people it's useful especially like you said for vacation you want your baby to be as safe as possible.
I don't have much advice or really any experience with them.
Maybe someone else actually uses them more frequent.
But the sling/tote before the pink one is really cute