I've looked at the site of the hori hori manufacturer in question, and I saw a pretty pointy blade with a partial double edge (halfway up from the tip). Where I live, in France, that constitutes an illegal blade, as any kind of sharpening along the spine (including sawteeth) counts as it being a stabbing weapon. I also have a hori hori (different brand), hollowish thick trowel blade, one somewhat sharp edge, the other having sawteeth for cutting through nasty roots in the ground when you are preparing a planting hole or weeding. I can understand why such a tool can be mistaken for a bladed weapon by anyone, including urbanite police officers who have little or no experience with gardening or farming. Walking on a public street with it on display is a bit dumb.
France is a bit less paranoid concerning carrying knives. Non-locking folders are usually OK (like the famous Laguioles and Opinels that have been defined by the courts as 'traditional culinary tools'). One-handed opening/auto-locking blades will get you in trouble though, even if part of a multitool. But don't carry any sharp object with you if you enter an area where a demonstration is going on, as police will check your bag, and they have a generous definition of 'weapon by intent' - i.e. a street tile can legally be a weapon if you bash someone's head in with it or throw it at riot police.
I live in a very rural area (lucky me) and use largish cutting implements a lot to cut down prickly bushes, trim hedges, clean out bramble along roads and trails nearby to facilitate access to berries, and whatnot. You can find me on the public road along our terrain while I am doing such things, often carrying a Skrama Bush Tool (many here will know them, from Finland, like a seax, 240 mm blade, one of the best large chopping knives ever) in a milgreen molle sheath across my shoulders, along with a sizeable saw in a similar sheath, and while likely wearing kaki multipocket pants, a UK Soldier 95 desert camo shirt (because it's dirt cheap surplus and it's dirty work), and possibly, when it's a bit colder, a milgreen smock-style jacket. Add wraparound dark-coloured safety glasses, an orange baseball cap/helmet combo and you get the picture. In any (sub)urban area the neighbours would probably think I'm a weirdo. Here, I'm just one of the people who work outside. Local hunters passing in their 4x4s often start waving at me before they realize I'm not one of them.
If our village trail-clearing group comes into action to clean up tourist paths, you see quite an arsenal. Sickles, shears, saws, axes, chopping knives, basically anything with a sharp edge. So nobody even blinks when they see me working with my edged tools.
The gendarmerie officers in the area really don't care. They know they could arrest the entire population if they started searching them for bladed items. Including their colleagues.
But I would never openly carry my edged tools on a public road in an urban area. The 80 percent of the population who live in cities are just too paranoid for that.