How does a marzipan knife work?
Judging from the picture, the knife gets thinner towards the spine after reaching a point of maximum thickness somewhere in the middle of the blade. This means a straight piece of sticky food cannot stick to all of the blade face at once unless it actually bends to conform to its curvature - and marzipan is a rather stiff medium. Also, since the food will not be stuck flush to the blade face at spine height (levered away from it by the thickest section of the blade), it will be much easier to grab and detach from it.

Also, it appears the surface finish has intentionally been left somewhat rough, further preventing adhesion effects.

If the spine is actually sharp, package this diligently when transporting it in public - a double edged knife tends to be interpreted as a weapon and not as a tool under some countries' laws.