I've actually run Velotha's Flock at a con, and it went pretty well. I played with the rules for cards, rather than dice, though the setup is more or less equal for both. Now, obviously I made the game and I'd already done playtesting on it, so I had a lot of experience and other benefits going in, but I think we had a three or four hour time-slot. Some people showed up late, but we still had a good time by the end.
The mechanics are pretty simple: it's a d12 roll at-or-under result for success (on cards the face value of the card replaces the die roll), with a d6 for complications, and you don't need to make them super-significant all the time; I usually just give extra success when it's happy. With cards, red suits indicate a beneficial result, black suits a mundane one. I have a two-page condensed ruleset which covers, I believe, 100% of the game mechanics. They're a little streamlined, but so is the core rulebook. The condensed ruleset about 850 words long, but 150 of those are the overviews of sample characters.
The setting is where things get tricky, but I always focus on the symbolic stuff when I start players with Velotha's Flock.
You have were-ravens from another world that have come to our world.
They are searching for the Promised Land, based on a Prophecy that some don't believe anymore.
They're hunted by Lucifer and an abominable god from their homeworld.
That gives players enough room to run with it. Character creation tends to take a while, because it's a "choose packages" style game and there's quite a few options available. Fortunately, I have pre-mades. The pre-mades include rules for their abilities as well, so you can run the game with the two-page rules and the sample characters.