Let's hope that no politician reads thiswish they would at least just come down to a size limit for fixed blades that can be " concealed ", and I only say this because a little is all they'd ever give if at all.

Main problem with those kinds of laws is in definitions. Let's say that you can basically carry any legally acquirable kind of knife, but you have to be in situation typical for it's use. But law doesn't give you literally any example of this type of situation.
Then the minimum concealable length sounds kind of crazy. Lots of knives can be carried absolutely concealed regardless of length. You would then basically legalize long blades to be carried concealed. And many knives are what would you consider small knives. I can assure that you can do way more damage with something like Glock FM 81. That think could be easily used to chop someone's hand right off. I don't think you could do that with a puuko. Only good regulation would be just to ban carrying concealed knives without a permission to do so (police officers, special ops...). And after all that you've got the fact that you would need really good definition of concealed carrying is and not letting court or police officer decide. Is concealed carrying carrying knife in your backpack? Is concealed carrying carrying a knife in your pocket?