I recently ran out of Steam Way Fiber Refresh acid rinse detergent (pH 4.0-5.0) so I picked up a gallon of Clearwater Rinse (pH 2.7-3.3) which also contains encapsulating polymers. I didn't notice Flex Ice containing encapsulating ingredients.
I have not tried it yet. I don't use acid detergent rinse often. I rinse a lot to remove not only the soils but the prespray and have not caused myself any issues some have claimed with their experiences. If you remove the prespray it follows that you should not need to neutralize it. I don't use super high pH tlc often.
From the comments here it seems clear that it is hard to beat the cleaning performance of a well formulated alkaline product with an acid side cleaner. Of course there is more to cleaning performance than the pH of a product.
If the pH reading on the fiber after cleaning is a little alkaline there is usually nothing to worry about on synthetic carpet. (some tap water can be quite high in alkalinity) It's more important to me that the product does not contribute to resoiling, something an alkaline or acid product may or may not do.
I have been bucking the board trend by using a liquid prespray and a power rinse detergent. It seems most use a powder tlc and liquid rinse.
The recent Cleanfax article by Tom Forsythe was interesting. If I remember correctly one of the advantages of powders for cleaners was that it might be more cost effective, but not sure if that equated with cleaning better than a liquid. (I should go re-read it)
At any rate, I will try Flex Ice when I get to a distributor that carries it. Sadly, Cleanquest in Concord, CA doesn't seem to carry Bridgepoint.