I have two Skilhunt E3A lights, one regular cool white and one high CRI neutral white, both with slate blue color anodization and purchased from AmazonUS in early December of 2020.
Both lights have O-rings that measure and look like the O-rings in your posts. The supplied O-rings are too loose and stretchy in my opinion and can be pushed out of their groove if I am not careful when screwing the head onto the body as you have also experienced.
Compared to other AAA sized twist lights I have (Sofirn C01S and Glaree E03), when using only one hand, the regular cool white E3A is somewhat difficult and the high CRI neutral white E3A is almost too difficult to twist. I switched the O-rings between the two E3A lights and this did make a difference convincing me that the specific O-ring is responsible for the operating torque required.
I measured the outside diameter of each body at the bottom of the O-ring slot (0.458" average O.D.) and the inside diameter of each head where the O-ring mates (0.512" average I.D.) and found no appreciable physical difference between the two lights that would affect the operating torque contribution from the O-ring, further convincing me that the specific O-ring is what makes the difference.
I prefer twisty lights that are difficult to twist so they stay together as one unit and compared to other twistys I own, the E3A has more turns of thread engagement which also helps with this and the precision tight-fitting threads between the head and body allows the E3A to be "turned off" and be "completely locked out from turning on unexpectedly" (due to bending or axial forces at the head / body junction) after less than a quarter of a rotational turn from the "on position" which is less and better than any other twisty I own.
One cosmetic difference between my two lights, is that the regular cool white E3A does not have the white circle with the plus sign engraved on the body to indicate the correct battery polarity orientation.
This same light also has an area on the head threads that is not completely anodized but I do not understand the internal construction of the light's electronics well enough to know if it will continue to function correctly and be able to turn off instead of always being stuck on if the adjacent anodizing on the body threads wears sufficiently to the point where the light's body is electrically shorted to the head.
While I prefer the compact form factor of the Skilhunt E3A, I use my Sofirn C01S and Glaree E03 lights more because of their additional low brightness mode which is especially useful as a passenger in a car or while inside a dwelling after other's bedtime.