Hi, Justin! I own an Oktava MK-012, with omni, cardioid, and hypercardioid capsules. Mine was modded by Michael Joly, so it's less noisy than stock ones. (Be sure you never get an MC-012, those tend to be Chinese knock-offs.)
The MK-012 is best known as a low-cost condenser for use in the studio and for dialog. It's often called "the poor man's Schoeps," but in my opinion, there's no comparison. Now, that said, it does deliver big bang for not a lotta dosh. I was about to say what I think it's good at, but then realized that everyone's got their own opinion. Remember: It won't sound like a $2000 mic. But, you might find that it sounds better than a $250 mic. (Yeesh. That was vague.)
What's not up for debate are its frequency characteristics. The omni capsule is kinda flat, the cardioid has a big high frequency dip, and the hyper even more so. That's not unusual for condensers of those patterns. However, it's pronounced when you A/B the modules.
I think that MK-012's are great tools for most professionals, even if it's simply to have a decent condenser mic that's "expendable" compared to higher-end models. I've attached mine to all sorts of sketchy mounts and moving objects without fear. I have absolutely used it in effects gathering, and on the human voice. However, for my personal taste, the noise floor is too high for subtle effects gathering, even with the Joly modifications...too much hiss. For louder sound objects, it's just fine (the 3-capsule kit usually comes with a -10dB pad).
I also own a Røde NT4. If I were going to do XY recording of natural ambiences (birdsong, crickets, etc.), it'd be no contest: NT4 for the win. Even if I were to do A-B or Jecklin Disc recordings for that same use, I'd probably even then get two Røde NT5's instead of an MK-012 (options would be way wider at higher budgets). If I was gonna put a condenser downrange of a gun, get some warm vocal tones, record bright cymbals, mount it to a vehicle - but still wanted good sound and not some throw-away mic - the MK-012 would get some use.
Just one person's opinion, though!