The first thing you need to decide is which hand you are going to use for what.
I started out with the technique that most people use. The right thumb pushes the cylinder release, the left fingers push the cylinder out, gripping the frame. Turn the revolver barrel up and hit the ejector rod with the left thumb, tilting the barrel downward when you finish. While doing that, grab the speedloader with the right hand. Insert the speedloader, twist the knob, discard the speedloader it, and close the cylinder.
I switched hands and noticed an immediate improvement. As before, the right thumb pressed the release, the left fingers push the cylinder out. However, the right hand maintains its hold on the pistol grip, while the left hand turns up and pushes the ejector rod with the palm (I don't tip the revolver down, as I find that full length ejectors kick the empties out just fine with a brisk tap). The left hand grabs and inserts the speedloader. Depending on the revolver and your hands, you can hold the cylinder still with your trigger finger, through the frame, or you can place your left pinky on it. Twist, discard, and close the cylinder.
Theoretically, the first method is faster. You eject the empties and grab the speedloader at the same time. I find the second method to better for me, because I can keep my right hand grip throughout and it seems more streamlined.
Now, one issue with HKS speedloaders is that twist. Twist too hard and the rounds with bind up. Trying to twist back to a straight position will most likely end up binding the rounds the other way. I wiggled the speedloader and that worked for a while.
Then I retired the HKS speedloaders and started using Safariland Comp speedloaders. If Safariland offered as many models as HKS, I wouldn't see any reason not to use Safariland. They hold the cartridges with no wiggle and there's no twisting. Grab the whole unit, push it into the cylinder and it releases the rounds. I suggest you try one. You can, in my experience, be fast with an HKS. You can be faster with a Comp.