Jason B. and Wowbagger, thank you for your replies and good info!
The video was very informative. He does a good job reviewing and gives the top rating in this group, and others, for cutting speed to the 200 grit Suehiro Debado MD-20, which is "splash and go". Interesting that he says the Shapton Glass 220 cuts faster than the Pro 120, but unfortunately doesn't say why. I'm glad to have found out that both Jason B. and the video recommend the Glass over the Pro, as the Pro is what I would have bought if I hadn't seen these posts.
I was also glad to find out the Shaptons were all "splash and go". I generally avoid waterstones because they are too messy and high maintenance for me but of course the "splash and go" type would be much easier to use.
I watched a video on the Naniwa Pro 400. They require a pre-soak, so are not really "splash and go", but I was surprised to learn that they don't load up. I've never heard that said about any stone.