Not much of a Spoiler but meh.....

So I just found this piece of Awesomness ;P.... and now I'm tempted to keep it. So help me to decie

A. Should I keep it and make my life easier with picking up all doors around Skyrim (I plan only to keep it untill I get done with all other quests, and after that I'll return it and finish of story line)
B. Should I struggle with lockpicks and stuff w/o this "key"?

Basically I can't decie, I got this far with thiefs quest line and I want to finish it, but on other side I wonder if I should keep it.... afterall it's awesome thing to have.

Where did you find it?

Use the spoiler tag in the "Orhter Styles" drop down if you feel like it.

I'm pretty sure it's only a quest item in Skyrim.

I believe I seen a perk in the lockpicking tree that makes them unbreakable, so essentually, the same could be achieved with enough patience (and points in the lockpicking skill, of course)

It's not "quest only item" I can lock pick any door with this key.
But what I've meant is, after you complete last quest of this, you need to return key back to won't tell you the name since it's spoiler. Basically if you get done with quest The Key is gone for good.