I could have bought Si Tech QCS when I had rings installed on my old Waterproof suit. I thought the Kubi were worth the extra money, so I got them.
I liked them so much that when I ordered my first Seaskin, I got the Kubi again. I still think they are worth the money.
They have different size rings, so you can get ones that are pretty much exactly big enough, without being any bigger than necessary.
You can use them with dry gloves and have wrist seals also, or not. Your choice.
They are machined aluminum, so they are very durable.
When not wearing the dry gloves, the wrist ring on the suit does not have any exposed O-rings.
The fully assembled Kubi rings, with gloves on, are less bulky than any other option I've seen. I.e. the length of your forearm that is taken up with the ring assembly is relatively short.
If I didn't get Kubi, I would get a setup that allowed me to use the Waterproof Ultima rings. They are also good. But, they sacrifice most of the details I just listed, in order to save some money. Plastic. One size fits all. Exposed O-ring on suit sleeve when gloves are not attached.