[fernando]

I do subscribe sources stating that, the basic purpose of this wile was to fool inspection on the legal length. An actual measuring verification would potentialy only take place if the owner walking on the streets carried a sword visibly longer than allowed, at the eyes of authorities. On the other hand, their encumbrance while sheathed or in handling was a minor factor, comparing to the advantage of having a weapon with a longer reach, when dealing with less ethic street fencing. After all, full length 'off mark' swords abounded, despite royal restrictions and, those yes, were far easier to detect by the law, creating a bigger problem to conceal, when going out to use them.
Now, whether the mechanism/s of these extendable swords was/were solid enough to be reliable, is another story.

.