That's ok - 6cm blades are allowed. You can also carry it in a cabin luggage anyways.
realistically any broken glass bottle can be used as a blade.
Realistically, you could bring a nub of copper or steel or antler, and your glass bottle, and knap an excellent knife in a few minutes.
Whether they are allowed or not, probably depends on the place.
In Germany, at Frankfurt, I had to dump in a garbage bin a smaller Swiss army knife, to be allowed to pass.
I had it because my high-speed train of Deutsche Bahn had arrived more than one hour late, so there was no time to check in my luggage.
After losing the knife, I ran through the airport towards my gate, but I arrived there a few seconds after the gate was closed. Thus I had to spend the night at a hotel and fly next day, despite losing my knife in the failed attempt to catch the plane. Thanks Deutsche Bahn !