VPI Record Cleaning - Does Bidirectional cleaning really make a difference?

Wrong. This is no substitute for bidirectional motor. And unless the record is very dirty you don't want to scrub it, if you do you push the dirt deeper into the grooves. You move the brush rather gently while applying fluid, agitate a little. And Disc Doctor brush is better than Mo-Fi.

Okki Nokki is $500 from the distributor and it does both direction. Has pretty good vacuum too. I use it with Audio Intelligent three step cleaning system with excellent results. I read here that bidirectional does make a difference.
I did not compare it to VPI.

Taters,
You are probably right.

I would assume that some dirt particles are abrasive.
I only tried Audio Intelligent three step so can't compare to other fluids.
I also had a few records cleaned by Audio Desk ultrasonic with pre-cleaner and water on VPI 17 before that and double rinsed with water and vacuumed after. I did compare the same albums the same pressing with the records cleaned by me on Okki Nokki with Audio Intelligent, double cleaned and double rinsed with water each time.
I heard no difference, both were very clean. However, I don't have a high resolution rig so perhaps there is a slight difference. Still, my system is very sensitive to small changes of whatever, so resolution is not bad at all.