These work best in bathrooms that do double duty, where you're doing makeup at the sink with bad overhead light and no other option, or in a hallway or bedroom that needs one good mirror rather than a mirror plus a separate lamp. If your bathroom already has nice windows and good side lighting, you probably don't need one. And if you rent somewhere with a mirror you can't touch the wiring on, check what you're actually allowed to swap before you fall for one.
Size is where most people get this wrong. A mirror that's too small over a double vanity looks like an afterthought, and one that's too large for a tight powder room just reflects how tight the room is. The rule of thumb is to measure your vanity width and take off about four to six inches on each side, so the mirror doesn't stretch all the way to the walls. Height matters too, you want the bottom edge roughly four inches above the faucet, not jammed right down near the counter. Measure twice before you drill anything, because these are heavier than a normal mirror once you add the light housing, and a stud finder is not optional here.
On finish, the frame color matters less than the light temperature, and this is the bit nobody tells you until you're standing in your bathroom looking faintly jaundiced. Warm light flatters skin but makes a small white bathroom feel yellow and dated. Cool light is crisper for makeup and shaving but can feel clinical if the rest of the room is warm toned. The best ones let you adjust between the two, and that dimmer function is worth paying for, because a fixed single temperature is a gamble you only find out you lost after it's already on the wall.
The cheap versions have a thin plastic light ring that yellows within a year, a dimmer that only has two settings, blinding and off, and edges that buzz faintly at night like a fridge. A good one has an even, shadowless light along the whole frame, a dimmer that actually dims gradually, and a frame substantial enough that it doesn't flex when you clean it. That difference shows up every single morning, which is more than you can say for most bathroom upgrades.
Where these fall short is anywhere you need a mirror to just be a mirror, a closet door, an entryway, a big statement wall where you don't want a light source competing with your actual lighting plan. They also don't love steamy, poorly ventilated bathrooms, condensation and electronics are not friends long term.
If your bathroom lighting has been bothering you for a while, this is the fix that actually changes how the room feels every day.