Can we have a serious conversation about how many brands have used that first stage?Apeks doesn't hold patents on those designs, but they are blatantly knocked off. Imitation is the best form of flattery, so I don't see an issue with it, and without patents, there's no legal reason not to.
The parts between the HOG D1, now the Deep6 thing through DGX, and the Apeks DST do in fact interchange *did it for the first time myself 7 years ago....*
As far as baseless aspersions, it's known that the design was copied from Apeks, you can't really deny that, so that takes care of baseless, but on the aspersion front, it's not an attack on anyone at all. The design that they use is open so long as you don't have any ethical issues with copying someone elses design. Frankly I see no reason not to, and if they wanted to patent it to protect it, they would have. They didn't, so in the best interest of creating the most versatile regulators, it makes sense to follow in their footsteps
Of top of my head there is HOG, DGX (via Deep 6 ), IST, Scubamax, Salvo (RIP), Sea Elite, and host of brands that haven't gotten any traction in the US
Now, other close copies of that reg? XS Scuba, Hollis come to mind right away..I know there are more