I have read the Laboratory chapter again and again and it looks like Free virtues may be gained in a day without need to be balanced by a (free) Flaw.
Am I correct ? Would it mean the Free Flaws are here for flavour or explicit mechanics ? I don't see why I would WISH to pick one for my lab. I could consider to choose one or two for their specializations though (and I may HAVE TO choose a Free Flaw, like Dirty, Empty, or if my Upkeep is too damn high).
Are they some other official supplements displaying laboratory Virtues/Flaws ? (Outside Covenants).
Free flaws are there for flavour and to reflect any restrictions imposed by the structure of your covenant. Not all are actually serious flaws, and some are bonuses which come with drawbacks.
For example, "Disguised" isn't a flaw - having the lab concealed may lower your Aesthetics and reduce your reputation, but is useful for a security-conscious magus. "Empty" is necessary for magi who plan a massive lab, but haven't been able to fill it yet. "Low Ceiling" may be forced upon you if your covenant is situated in caves or tunnels, forcing you to dig a lot, or if your lab is below decks on a ship. Likewise "Exposed" if your lab isn't fully roofed.
Unstable is necessary for labs prone to movement - which those onboard ships or flying towers or put on a cloud will be.
Some are questionable choices (damp, decaying, deformed, disorganized, gaudy, subterranean, exposed, vile surroundings) which offer a modest bonus in exchange for significant compromise in cost and upkeep. Still, they're free so they don't take up space.
Some make your lab cheaper (inferior equipment, inferior tools, lousy ingredients, missing ingredients) at a cost of worsening your lab work. These may be necessary for impoverished covenants.
As an example, a Merinita with Strong Faerie Blood who intends to follow the Becoming mystery as soon as they can may not worry about decreased Health in their lab, and so a Damp lab in the Vile Surroundings of a swamp could give them 2 points of Aquam bonus for the cost of 1 point of upkeep and -2 to aesthetics and -3 health. If you don't care about Aesthetics and Health, it doesn't look so bad.
Or covenants that are just starting out, and have yet to get their finances in order.
any magus/maga under 35 and not suffering from wounds, can simply ignore the Health modifier.
Will you be fixing that damp corner when you get older? Most certainly!
But for now, it's no big deal!
I've also seen free flaws as either the hook for a story (Why is there a damp corner in my lab all of a sudden? We're on a hill, and the room below me is dry enough!) or the results of stories that were less than succesfully resolved CoughUnroofedCough.
They are not necessarily gained in a day or gained at all. But if gained, they do not need to be balanced.
You might not wish to, but sometimes you don't get a choice, depending on your saga. Perhaps you are stuck in the worst lab at the worst covenant. Or perhaps you have had 100 years before play to have exactly the lab you want.