You won't beat the Idahone for the price. As far as Shaptons go, if you wanted one for touchup, I'd recommend something from the pro series if you don't have a GlassStone base. Shapton Pros are splash-and-go, and also have better height to fit into another stone holder if you don't feel like using the one that is included. I use it sometimes, sometimes I don't, it works great either way.
Small conversation on the Green Brick.... I don't ever really soak that stone. About 1 minute under running water, lap it, splash again and good to go.
Depending on the edge and the steel you are using, 4,000 could be a bit fine for touch-ups. What kind of work are you planning on doing and what kind of knife will you be using will determine what you should be using for touchups IMO.