OK the test
I made a test with my tooth sword breaker and a 1620 rapier.
I did not do the full break test yet
when the rapier blade is between the teeth, it is really easy to hold the blade firmly without any tension. if you change the angle a bit the rapier blade is in a fixed position. it is very difficult to pull it out.
I also do think that a thinner rapier blade can break if you make the right move with it.
however I do agree that the main purpose of the left hand "sword breaker"
is holding the opponents blade for making a counter attack.
re: spring dagger
with this dagger it is not possible to hold or to break a blade.
I think the use of this dagger is to increase the "blocking surface".
re: 2 Handers zweihander
I think we have to open a separate thread there are a lot of stories and statements about the use of this interesting sword.
regards from Holland