What really should be illegal is to make laws that regulate the physical properties of objects, without a guideline on how to determine these physical properties.
We have a similar issue here in Norway, where they recently introduced a general ban on knives with blade lengths over 25cm. It's a silly ban because if you need a knife above that size you can still legally buy, own and use such knives without any paperwork, so it's basically just a smokescreen to make it appear like our politicians are addressing a tiny knife crime problem related to a very particular part of our largest city, where some gangs supposedly has taken a liking to large knives. It's already illegal to carry these in the city, so yeah.. just stupid.
What it does though, is potentially getting regular, unassuming, well meaning people into a legal squeeze. The law only states a limit of 25cm, with no additional guidelines on how to measure or interpret this limit.
Obviously just setting the limit at exactly 25cm indicates that this wasn't worked out by smart people with proper insight and knowledge on the topic. It seems arbitrarily selected because it was a nice and roundish number and a length that should be sufficient for most people.
Never mind that knives are commonly designed and measured using inches, and that the closest even number in inches is 10" which equals 25.4cm.
Now, that may or may not be just fine. As long as it's stated as 25cm and not 25.0cm, by common math practice, that should actually cover any length up to and including 25.4. But will it? No one knows. Even if, there's not much room for error, that's for sure.
And is it the makers stated length that should be considered or the actual length of the specific sample you received? You can't measure a blade before importing, so who is responsible for production tolerances in this case?
And like with the UKPK, how is blade length measured?
Sorry for the rant, I just get so fed up. The purpose of a rules based society is to facilitate cooperation and competition on even and predictable terms. Not to make criminals out of good people.
With regards to measuring blade length, there's probably no bullet proof way to make a guideline that will have a perfect outcome every time, there's just so many blade shapes, grinds, blade features and handle designs, and someone will no doubt come up with new designs just to utilize some loophole. If we can just accept that and focus on not making criminals out of people with good intentions and make guidelines that are easy to understand and that clearly indicates that any doubt should benefit the accused - you know, these small details that used to separate a free democracy from banana republics and dictatorships.
One step in that direction is to only focus on edged blade length (sure, that's also subject to definition, but still clearly identified on most knives). In my opinion, nothing creates more confusion than where the blade actually starts. Whereas the end/tip is usually more easily identifiable. This will become much less of an issue if any part without a clearly defined edge or swedge is defined as handle.
So basically, if this Izula is considered a 2.63" inch blade length and not 6.25" (which I suspect most people, even police and law makers will agree on):
then this (UKPK) has (and should legally be considered) a 2.58" knife blade too:
