Re: "My keychain has 2 sizes each ..."
Re uk/leatherman. I keep mine in my car.
IF they have a locking blade, we can't carry them technically. It's not black and white. we are "allowed" tools. So it's all about context really.
If you're a local scrotum caught with one at 11pm, i'd not fancy your chances. if you're not a little scumbag, and you have a reason/justification to be carrying it, that is supposed to be fine (i.e. a workman with one in a bag of tools, would be different to as hooded youth out at night. It's a bit murky.
Any model without a locking blade of over something like 3 inches, and you're fine.
Blade length+lock is what it goes on.