I've had my Kubi gloves for almost 3 years now. The first 1.5 years or so I had the suit side rings that just clamp onto existing suit seals. Then, I sent my suit off to Dive Right in Scuba and has the Kubi permanent rings installed on the suit.
In all that time, my hands have only gotten wet once. That was after right at a full year, when I finally got a pinhole in one of my gloves - the Ansell G17Ks that cost about $2/pair, by the way.
For sizing, I printed out the template of rings that Kubi has on their site and used it to cut holes in a piece of cardboard. That allowed me to determine that 80mm rings would work for me. I'm 6'1" and in motorcycle gloves, I usually wear size L - sometimes XL, depending on the glove.
I use SmartWool glove liners or the Pinnacle Merino wool liners, depending on how cold the water is. Those, with the G17K gloves give excellent dexterity.
I ordered a new Seaskin drysuit last week and ordered it with the Kubi rings installed on the suit. They are not cheap but they are totally worth it, to me.