Here's a pic of water being tested for PH. I've done so many of these PH tests on soaps and chemicals for work that I just assume that water is a 7. Water usually tests out somewhere right around 7 depending on additives.
I was a little surprised to see that the Meguiars is as acidic as it is. It's a little hard to tell from the pic but in person it looks like between a 5-6 reading. I'm sure that the acidity helps the Meguiars shine. You should be OK with using the Meguiars just don't spray it on the car, leave it on without wiping, and let it sit all day in the sun. I get much stronger acid and alkaline readings from some of the cleaning chemicals I test. I've seen readings at both ends of the scale. A couple of points up or down from 7 is relatively mild. The 4 I got with the Mr. Clean is comparable to the ratings I have gotten from bargain basement gallons of soap from Auto Zone.
Jack, to test I dip the test strip in the product [or spray product on the strip] and let it sit for 15 seconds. The readings can get screwy if you let the strips sit for much longer than a minute. I took the pictures within 30 seconds of dipping/spraying the strips. I coated each strip with product, set it down, and coated the next strip so that all were coated within 15-20 seconds of each other. Then I waited around 15 seconds more before I took the pics.
Victor, Simple Green is alkaline. All alkaline grease cutting products will show a green or blue reading. The further you get from 7 in either direction, the stronger the cleaning power will be [and the more dangerous the chemical is]. Most companies use mild alkalines because of the grease cutting power and because acids will harm glass and aluminum faster than alkalines will. The main advantage to using an acidic product is the brightening effect an acid will produce. Acids are also a little easier to rinse off which helps prevent the spotting.
Painter, I have found that my California blade has really softened up since I use it often. I always wipe the windshield first to get the blade moistened. I run my fingers or a towel over the blade after wiping the windshield to make sure there aren't any little pieces of grit adhering to the edges. No problems with scratches from the blade that I can see.