What it is
The Blue Yeti is USB Condenser microphone created by the company Blue (so I guess that makes the mic the "Yeti"?) They seem to be popular among streamers and content creators, likely because they're very easy to use; you just plug it into your USB slow and you're ready to go. It has two knobs on the back end of it; one to set the gain, and one to set the "pattern" (stereo, omnidirectional, bidirectional, and cardioid), which affects which direction/s the mic records from. It is capable of recording left and right audio channels separately, which is nice. It also has a knob on the front for volume, it comes with a stand, has a screw for a standard mic mount, and allows you to plug your headset/earphones into the mic itself so that you can "hear" what you are speaking as you talk. A mute button and a volume knob are on the front. It does not come with a shock mount (some three-pin condenser mics do, oddly enough) or a mic cover, I had to buy that separately.
Review
I bought it because I desparately needed a good microphone. I bought a headset with a mic, and it broke. I bought another headset with a mic, and it's a really shitty mic. I then bought a $30 three-pin condenser mic, but I didn't realize I needed a power supply for it, and those fellows are not cheap by any means. I eventually decided that, instead of being cheap and continuing to buy a bunch of crappy mics in hopes that one of them would work, I would just buy a singular really nice mic and save myself the money and time.
It is crystal clear, though; very crisp, a lot crisper than the three-pin condenser mic that I already owned. I know for a fact that people can make out my voice okay and that my mic isn't maxing out when I talk. It is reliable; I just had to plug it in and it worked, I didn't have to fiddle around with technology. I mostly just use it for Discord and Zoom calls and voice-recording, but it's nice to be on Zoom calls and know that people can make out my voice, or that I'm not causing "earrape" with my gain.
The major complaint that people seem to have with the mic is its longevity; it's not renowned for breaking quickly, but it's not renowned for its longevity either. That being said, a lot of idiots on Discord and Reddit seem to think its a good idea to keep it powered on "at all times", because it is good for the item to be running electricity without cessation through something that needs electricity to run. (Spoiler alert, electronics need breaks every so often, if you run them constantly you will fry them out.)
The microphone itself feels very nice; solid matte metal body, it's heavy, it feels well-constructed. (With tech like this I always wonder if they just weigh it down to make it feel more expensive, because my other condenser mic is light as hell.) I would like to get a shock mount for it in order to save desk space and further protect it, but I don't really want to spend the money. I'm just baby-ing it as much as I can, trying to set it down as slowly as possible, and not to bump it.
The online price fluctuates a lot: for a while the regular (non-mini) mic was $80, now it's ~130, I got mine for 100-ish. If you want to snag one for cheap, keep your eye on it and it'll probably drop eventually.