This is what I was worried about hearing, I would guess it's only around .8mm thick around the motor cutouts, incredibly thin for aluminum to retain trueness. Ironically Xray sells a 1.5mm thick Flex Alu chassis that they state in the description that it's strictly for competition races only and has reduced durability. This bleeding edge advancement in chassis design has its limits for independent drivers like myself that can't pocket $130 USD chassis over a small oopsie, I'd have preferred they offered a MTC2 carbon chassis option. Not sure if I want to "upgrade" to the MTC3 just yet. Maybe see if Mugen does something down the lines like the steel chassis or a MTC3R with a carbon chassis option.

I developed a 2mm carbon chassis for black carpet with a specific fiber orientation that mimics the performance of aluminum or steel depending how you tune it. It doesn't tweak and improves polar moments of inertia. I did one for the A800R and currently have a pro driver running my X4 version. These super thin aluminum or steel chassis is not the correct development path. You're not addressing the real structural performance issues by doing this. Making these super thin chassis and tooth pick top decks is just a band aid to the inherent design flaw on some of these platforms. The CG impact between all the chassis variants is negligible when you consider the overall weight.

Youll split the laminations on a 2mm CF chassis easier then you will bend an alloy or steel chassis.
You may not crack it visibly but at that point your CF chassis will be a wall trophy.
And thats if you dont rip the 90* screw heads through it first.

As I get people in the office looking at me funny for the reason why I'm laughing

As a datapoint: 1.02mm

Are you talking about these screws?

Regarding the choice of C-clips (CTW-28) or O-rings (OR4x1) to hold the plastic lower arm inserts, is there a performance or maintenance reason to use one over the other?

Nope.
Just preference.

Maybe, so far so good with our design...I've got the secret sauce and you don't.

local racer said he bent the chassis in a rash during the sunpadow race in china few weeks back

Another friend with the MTC3 was crashed into on the straight when another racer jumped the track and nailed him on the left front. The front left was completely mangled and the chassis seems to be bent as well.

Something has to break at some point!

I am guessing you're machining chassis out of quasi isotropic CF plate such as dragon plate? I have wanted to try this idea for some time.

https://dragonplate.com/quasi-isotro...n-fiber-sheets

What are the pros and cons? Hard to prefer one over the other without knowing that.

Either you want to deal with the big C clip, potentially flying into the abiss when you put or take it off, or the ease of install from an O-ring but not knowing if its completely seated in the groove and potentially coming off. Not to mention it dry rotting and crack and fall apart after a few months and the arm coming off mid race..

When steel bends, it doesn't "spring" back (unless its spring steel). And if they are using steel as a means to make 1.0mm to 1.2mm thick chassis's to get weight down ultra low center of gravity but not weigh too much, all of these ultra thin chassis's will fold like a wet noodle ...LOL

If they offer a thicker 2.0mm aluminum chassis, I'd probably run that and just adjust where I can to make up for the increased height. Unless you're Jacob Cruz, Ron Volker, etc most of us club racers probably won't realize the benefit before we hit something and tweak it. A tweaked thin chassis would hurt our lap times more than just running a thicker chassis that's more durable. I should have all my kits, parts and option parts later this week so will be building one of them for myself to race later this month on a decent sized outdoor asphalt track. So we shall see how the chassis holds up to my driving. Jackson Raceway here in Jackson, NJ has concrete curbs but they're smooth if you ride them right

Aluminium doesn't tend to spring back either.