is the bike quip inner fender helpful in keeping the hollow middle of the ST cleaner?
That is the goal. While I have just installed it and have not ridden in the wet yet, It is basic physics that are in play, so I suspect it will do it's job.
It's probably not a big deal, but if you have the rear wheel off already, it is a quick install and I picked it up awhile back when ordering something else from the UK. Goes hand in hand with the front fender extender I installed to also help reduce spray on the undercarriage.