Alright, here it is. My original build from 10 days ago was the same thing but with a third Breaker the Magical Warrior and third Ancient Gear Fortress over the last two tech slots. I ultimately went with Magic Drain there because you lose to spells more than you lose to anything else, and it's a great disruption card against Koa'ki and certain cards in the mirror (which were by far the two most common match-ups I saw). Vampires and Buster were free with Unending Nightmare, Spellbooks were very difficult, and Heroes were easy if you didn't lose turn 2. Obviously some semblance of technical play comes up in the mirror, but overall it seems to be decided at the deck-building screen. I also found myself getting a lot more value out of Ancient Gear Wyvern the more I played, searching it off Geartown occasionally (like in this replay, where I was using Wild Tornado) to set up a stronger board.
Breaker is a great card in this deck and I think it's incorrect to play without it. Galaxy Cyclone and Planet Pathfinder are both bad, as is Double Cyclone outside the mirror. Middle Age Mechs also feels like the correct skill; having access to normal summoning Ancient Gear Reactor Dragon is very strong and I missed it when I was testing Sealed Tombs (which is the only other skill I would consider).
Activating two Ancient Gear Fortresses is not a bad idea as they protect you for a turn against targeting and destruction after you pop one.
Unending Nightmare is the best choice for popping your Ancient Gear spells because you get multiple uses and it isn't reliant on your opponent playing backrow like Double Cyclone.
Decent match up. With 3 Ancient Gear Fortress and 3 Ancient Gear Wyvern to search it Ancient Gear Reactor Dragon is protected against Koa'ki Meiru Maximus' effect. However I see Koa'ki Meiru Ice going up in usage as they can potentially pop Fortress with Maximus then pop Reactor with ice. However to do this cannot they cannot summon Koa'ki Meiru Sandman on the same turn to negate any backrow you may have e.g. Canadia. The Ties that Bind will also become more popular as they allow Maximus to beat over Reactors in Balance builds, but struggle when playing against the Middle Age Mech versions.
Good matchup. Unending pops DNA surgery disrupting Buster Bladers fusion combo but they can always go into Dark Paladin and Ancient Gears have no inherent way to get over it it's higher attack without use of Beatdown.
Strong matchup. With no inherent way to beat over Reactors 3000 defense and attack Karakuri must rely on drawing into Offerings to the Doomed or Enemy Controller, but we can consistently disrupt their drawing with Karakuri Anatomy using Unending Nightmare making this a strong opponent for Karakuri.
Unfortunately I didn't face a single Vampire player. Vampire Vamp will be an issue but Unending Nightmare can pop the field spell and Domain so I see it being a decent matchup.
Potentially a very strong matchup. Not enough testing yet.
Poor matchup. Spellbooks have an inherent out to Ancient Gears with Spellbook of Fate banishing Geartown and Ancient Gear Fortress before they can be destroyed. We also have very few monsters and cannot always swarm the board to overpower Spellbook of Fate's once per turn limitation. However Spellbook have fallen in popularity (although they may return during the KC cup) and are not worth building your Ancient Gear deck to counter.
This structure deck may be one of the most meta shaking structure decks we've had in a while. Ancient gears have easy access to Ancient Gear Reactor Dragon by destroying Geartown with any assortment of cards. The addition of Ancient Gear Wyvern adds needed consistency to this strategy as well as having decent stats; Ancient Gear Reactor Dragon sits at a formidable 3k attack and defense, which results in many deck struggling to remove your boss monster; Ancient Gear Fortress provides protection so that your AG monsters becomes untargetable the turn they are summoned, meaning they cannot be targeted by Vampire Vamp, Koa'ki Meiru Maximus, Paleozoic Canadia, or Enemy Controller.
The potential weaknesses of Ancient Gears are their inability to adapt and potential inconsistency. The deck is very reliant on using card effects to destroy Geartown which means card space must be dedicated to the monsters you want to search out Geartown, Geartown, the monsters you plan on summoning with Geartown, and possible protection for your monsters to ensure that your opponent can't out your boss monster. If AG becomes very popular, the popularity of Cosmic Cyclone may also go up which can banish Geartown and prevent the effect from triggering. Lastly, any combo deck running large monsters that they are unable to normal summon can have issues with bricking; if you lack any piece of the puzzle or have your combo interrupted then it is very likely that you will have to end your turn without a followup.
Overall I think Ancient Gears are promising but dangerously predictable.
Tell us your own thoughts on the structure deck in the comments below!