Hmm, self defense? Do they have hand-to-hand training?

There's a couple I've carried over the years - the current inexpensive single-hand-open style has been very convenient. I've broken the tip on them a few times using them to pry, but don't really care because I never spend more than $20 on one.

Being slim, they fit in any pocket (usually have a clip) without feeling like you're carrying something.

Was recently gifted one that holds 4 screwdriver bits and has a hex shaft to use them... And it's no thicker than the other ones I've carried.

So I guess it really depends on use-case.

What sort of budget do you have? $50 $200 $600? I tend to live in the budget world when it comes to pocket knives and would recommend something like the Civivi Elementum II which has great utility, is not aggressive looking, and provides a ton of value for the money.

It is very easy to get overwhelmed with choices. I would say pick something from a reputable reseller, with a decent return policy, and pick something that your partner likes the look of. If you have the budget, buy a couple different ones to get a feel for what is and is not good in-hand and in-pocket.

My perennial recommendation for this sort of thing is the Kershaw CQC-6K. Either the D2 or 8Cr14MoV versions, your choice. Normal people probably want the 8Cr one. Like all of the Emerson derived wave openers, it can be snapped open automatically when drawn from the pocket by way of a hook on the back of the blade. Drawing and opening it are not separate actions, or at least they don't need to be.

I hope your friend knows what they're doing re: trying to use a knife for self defense. I suspect they don't. As others here have mentioned, doing so is not for the uninitiated. It doesn't work like it does in the movies. Pulling a weapon escalates any situation and should not be done unless you're prepared to use it immediately and are justified in doing so. Pulling a knife and waving it around in front of punks on the street is, let's say, very unlikely to produce the results you want. Especially if you are not already of a stature to kick their asses to begin with, even without the knife.

A Leatherman tool and a can of pepper spray may be a wiser purchase.

In case anyone asks, my scale of self-defense options places a pocketknife squarely at the bottom well behind guns, bear mace, tactical airstrikes, swords, polearms, keeping a Doberman in your pocket, or just not putting yourself in sketchy situations to begin with.

Wouldn't try to defend myself with it but I love my Sog twitch xl. I've carried it every day for something like 10 years

Knives really aren't good self defence tools. Without training they are as dangerous to the wielder as to the attacker. Even with training running away is usually a better tactic.

Depending on jurisdiction carrying a knife as a (defensive or offensive) weapon may be illegal. There may also be restrictions on length, foldability, automaticity and concealability to carry a knife as a tool for no particular reason.

Are you aware of their local restrictions? If you let us know we can better advise.