TY has been pulling out Mech a fair bit. Most recently in Season 1 of the 2020 GSL, he used Mech in all three games in a winner's match against Dear.
I believe the power of this particular build is two fold:
It looks like a standard bio build for quite a long time. The Protoss doesn't 100% know it's mech until the two Factories go down after the 3rd CC and it actually gets scouted. I also feel that with the recent popularity of the early Marine/Tank/Banshee with bunkers push, it's hard for the Protoss to accurately predict that mech is incoming.
Generally, mech hasn't been fully "mapped out" in TvP. As noted by Artosis, each Protoss seems to have a different response when discovering mech. This can be used to great advantage as an opponent without a solid plan is usually easier to defeat.
The key points that I have identified in this build:
Gas first into Barracks expand
Scout with 19 SCV (this SCV is most likely looking for tech and pylon count)
First Reaper stays at home and looks for proxies
Reactor on barracks after reaper and constant marine production
First unit out of factory is hellion then tech lab. Hellion is used to deal with adept
Starport is immediately dropped on tech lab of Factory and a Banshee with cloak is started
After initial Adept pressure is held, Hellion goes and searches for 3rd Nexus. This is probably important to determine if an all-in is coming or not.
Banshee goes to main to harass while at the same time the Marines come forward to poke and most likely cause a distraction so the Banshee can be more effective. This also helps sells the fake bio.
Siege Tanks are being constantly built off Factory
After second Banshee is started, 3rd CC is started
At this point, it still appears as if TY is going for bio
After the third Banshee is started, HyperFlight Rotors is started. This is a very important upgrade as Banshees are used heavily for harassment throughout this game.
After third Banshee, a Raven is started. This is most likely to help take down Observers and to help defend against an early Colossus push.
After third CC is complete, TY expands in the opposite direction of opponent. On Golden Wall, this is more effective as access to this location is limited due to the Mineral wall.
Second and third factories go up as CC is floating to location. This now truly signals mech build.
One Factory is swapped onto Barracks reactor. Hellions, Tanks, and Banshees are constantly produced.
A Sensor Tower is placed to help detect any pushes. This is useful as mech is generally considered slower, and knowing in advance where a push is coming from is vital for positioning.
Once HyperFlight Rotors has completed, all the Banshees are sent out on the map as a hit squad, looking for damage. The speed boost they gain makes this very effective as they can easily fly in and out of locations. This also forces the Protoss to be on the defensive, allowing TY to macro up.
A fourth base is taken and the army is positioned near it. This works well because the Sensor Tower's provide vision on other attacks paths.
At 10.45, TY is maxed out with a blend of Hellions, Tanks, and Banshees. A decently formidable army if the opponent hasn't being preparing for this composition.
TY is continually scanning the main, most likely looking for any tech switches into air.
When 2/2 finished, the main army moves out for a push.
TY goes up to 8 Factories
Orbitals are built when floating too many minerals
The composition remains mostly the same, but I suspect this is due to Zest not transitioning to air. In the GSL match, TY introduced Cyclones and Thor's when an air composition was detected.
In my opinion, this build produces a composition that is quite strong. Especially if it catches the opponent off-guard. There are however weakness (as with any build/composition).
As seen in game 2 of the GSL matches (Vod below), TY died to a very sharp timing attack. This could've been attributed partly to being slightly out of position, but my experience leads me to believe that mech isn't super strong until high numbers.
TY also seems to constantly checking for an air transition. For obvious reasons, I believe this is important to discover as soon as possible. In game 3 of the GSL (Vod below), TY transitions to both Cyclones and Thors to great effect.
I hope you enjoy this build breakdown, and happy mech'ing!