Didn't it sound a good idea? Ketchup, mustard, mayonnaise in squeezy bottles, upside down so you can get the last dollop out.
Except that you can't.
Imagine the bottle as an armless torso standing on its head, wearing a hat the same width as its shoulders. The gloop settles down at the sides, where the shoulders are, but it won't come out of the comparatively narrow neck; and even if you take the cap/hat off, the neck is too small to get a spoon in. If you shake it hard it broadcasts gobbets of gloop, most of which don't land on your sandwich.
Grrrr. Back to ordinary bottles for me, and the wedging of same between heavier items to hold them upside down when nearly empty.