How small is too small? I'd say anything under about 36 inches wide works for a laptop, a lamp, and not much else, and if you need to spread out paper or a second monitor, you're going to feel it within a week. That's not a knock on small desks, it's just the honest ceiling on what they can do. I've built one for a home office that was really a hallway with ambitions, and the trick was accepting what it was for and not fighting it.
What separates the ones worth keeping from the ones you'll be replacing in a year comes down to a handful of things I check before I even look at the finish. Flip it over, same as I would with anything else, and look at how the legs attach to the top. Bolted into a solid block or a proper corner bracket is what you want. A few screws straight into particleboard with no reinforcement means the whole thing will start to wobble the first time you lean on it while reaching for a charger cord, and at a small desk, you're always reaching for a charger cord. The top matters more here than on a bigger desk, because there's so little of it to hide flaws. Real wood or a good plywood with a solid edge will take knocks and the occasional coffee ring without swelling or chipping. Thin laminate over fiberboard looks fine in a photo and starts peeling at the corner within a year, especially if the desk lives near a window or a radiator. Any drawer should run on metal glides, not just slide on wood against wood, because wood on wood sticks the second there's any humidity in the room, which in most rented apartments is always. I've seen small desks for not much money that got this right. I've also seen ones twice the price that didn't, so the sticker tells you less than the drawer does.
Where I'd steer away from a small desk entirely is if you're going to be at it for eight hours a day doing real work. There's no surface area to spread out, no room for a second monitor without it eating half your keyboard space, and the lack of mass means a lot of them shake when you type with any energy. They're built for checking email, writing a letter, paying bills, not for running a business out of. And be careful where you put one. Against a wall with a window right behind the monitor is a classic mistake, you'll be squinting at your own screen glare within a week.
A good one, in the right corner of the right room, is a quietly useful thing to have.