i use pencils and if you use the right technique on beading glass, there is no problem, you cant expect the water to do all the work for you
Bristles, bristle density, water distribution, water flow, water pressure, technique, this is what you expect to do all the work for you, and it does.
Back in the old days of traditional cleaning I have seen me when needed dipping my applicator in a puddle of dirty water when my bucket was too far away to go for a dip. Now the particular window was done to the same standard as every other window, but dosn't mean I would use this solution every day as my preferred solution.
Yes you can go out with a backpack (sorry for bringing backpacks into this) and a Vikan brush with pencil jets and get an excellent finish, but it dosn't mean to say that this is the best way of working.
Like a few people here have stated, lifting the brush to rinse separately is what they have been taught, much the same as the pencil jets, they have been taught to use them when they were sold them from their supplier. Now some people will try something different and it may take a slightly different technique, and they just think it is not as good because they are using their old technique with their new equipment, so go back to their old way of working.
Now obviously this dosn't apply to everyone, but it does apply to a lot. And it will also apply to people using fan jets as well when they try pencils, but again I say physics apply here.
Peter