Because I know myself well enough to know I might not come back later f I don't do it now, some thoughts:
On break tanks in general
This game was incredibly fast, even though I was expecting that. I would advise future GMs to 1) definitely get a coGM - I absolutely couldn't have run this without Devotary's help, and it was a struggle; and 2) make your rules as simple as you possibly can. Only test what you really need to test. Also, especially if you don't need to run the whole game, maybe consider a slightly longer cycle time
Several people commented that they don't play much anymore but would be happy to come back for Break Tanks occasionally since they're only a day, which makes me very happy - that's part of the intention of this format, and I'm glad it's working.
Issue-handling in a game this fast would be a mess. I'd advise players, if they have an issue, to ping the mod about it and then try to ignore it / don't interact with the player in question / whatever until game end, since we might be able to sort it out but might just not have the time to manage it.
These are going to be elim-leaning. I knew that going in, and might've done a 2-player game if there were only 9 or 10 players, but 12 seemed like too many for just 2 elims. Regardless, it's worth emphasizing that the chaos and speed of BTs will absolutely make it favor elims more, and future GMs need to remember to take that into account.
GMs should also not expect to have much time to do anything else while the game is running, especially during early cycles - later ones were much, much less stressful.
I was worried about only having 12 players (or 9, initially) at first, but... I can't imagine what C1 would have looked like with 20 players. I'm not going to say you should cap BTs at fifteen or anything, but having them be small is probably not a bad thing.
This game - balance / rules
This game felt pretty good to me. I did change it, as the committee members will know, from the initial idea of 'you get a power and have to use it the next cycle' to a more permanent style when I decided to use this particular flavoring with items and all. (By the way, credit goes to @Kasimir for both the flavor idea and the overall game concept.) I don't think it was a major detriment to balance, but I do think that version might've been more intuitive for people - it seemed like it was really hard for people to understand the delay between bidding and having votes added to you.
Having roleblocks use up the roleblocked person's item felt a little unfair to me.
The way I chose item types was by rolling based on a table (below) of probabilities, as many times as half the living players in the game (so C1 had 12/2 = 6 items, etc). I think those probabilities could be changed some without problems, and they reflect my particular preferences for what I wanted this game to look like (e.g. I made the kill % small because I knew the game would go fast with 12 players anyway). Moving the protect % up could be good in particular, partly since people tend not to actually use protects and partly because (as rules currently stand) using them is one-time whether you block a kill or not. I'm not 100% sure about the '# items = half of living players' part, and suspect that in late game the item consolidation might get bad, but there is a convenient mitigating factor in that the people with items are most likely to die to the exe.
For a longer version, I wouldn't be averse to having PM items last until one of the people in it died, rather than a single turn - I did that this game mainly to minimize the amount I'd have to keep tabs on in such short time. The 'you can specify a target when you bid on a PM item' was also a little wonky and made more sense with the you-have-to-use-it-next-turn version. It'd have been less of an issue with longer cycles, though, so me forgetting to set up a PM for 20 minutes wouldn't actually be a whole third of the cycle wasted.
Having bids able to go so high may or may not be a good idea - definitely part of the problem was differing starting assumptions (in fact I consciously went for that by using as few examples as possible in the initial rules so no one had any numbers to 'anchor' to), but I think lowering the max to half of living players might be helpful.
Probability table for powers:
PM - 30%
Bid up - 15%
Bid down - 15%
Roleblock - 20%
Protect - 15%
Kill - 5%
This game - flavor / regrets
I regret not preparing for this game better. I did have a spreadsheet (partly) set up before today, and a list of lots and lots of items, but I hadn't written descriptions for any of them - which meant I couldn't go into as much detail as I liked, nor add links to the many items with associated excellent past writeups / RP / etc. I'd like to go back and add some, but I think it's unlikely I actually manage that, so just to list - some of the ones with great writeups-or-similar were Discord (MR7), pandamodium (LG6/LG10), the doctor's coat (signups for QF7), Hael's head (LG18 at least, probably also LG19), the lerasium bead (LG19 aftermath), Wilson's Plate (LG20), and the lifeless rabbits (LG25). If anyone wants to find those links, you're welcome to. If anyone wants to rerun this game (and feel welcome to, I don't claim a monopoly on it!), this is an extremely messy sheet containing all the item suggestions I got (not just the condensed list I posted above).
Along similar lines, I would've liked to pre-write a bit of flavor for the writeups, especially for the first and last, beyond just the item lists. I was kind of visualizing it as a giant auction-house ala the start of Phantom of the Opera, and people were killing each other for items, or being killed by their own items (either literally for something like Slaughter, or just via being 'too powerful' for that person to hold). Maybe in a longer format.
Having the multiple items of a single type share the same pool was kind of weird and didn't work well - I think I'd want them to share the same pool still, balancewise, but might make it so a player can't bid on a specific item (or can state a preference but have some chance not to get it, so you don't get any information about anyone else's bids). Later I'll try and post a list of who ended up getting each item, since it's not specified in the sheet.
Overall, it was a really fun game to run, and I'm glad y'all enjoyed it as much as I did.