No chemicals on the concrete. I didn't want to use bleach (hard to find now) because I thought I'd probably have "spots" where bleach stood longer than elsewhere. We swept it all to keep all of the debris out of the yard. There were lots of tree seeds, leaves, etc on the concrete. Using the surface cleaner was a lot easier than using a wand which I have done once - what a job and it certainly didn't turn out as well as the surface cleaner job. Regarding the time it took, I had to go slower than I thought it would be. Not devastatingly slow but... Took awhile to get the speed down as to not leave streaks. Oh, I also did it in sections and then rinsed the section off along with the area where the runoff went to. Didn't want that dirty stuff sitting and drying in the sun on the unwashed concrete.
An 18" SC may have been faster walking but I couldn't find one with wheels from a company that should be in business long term. I think there was a couple chinese companies but how to get parts would be a problem. I do remember that they did not have grease zerks and I wanted what I bought to be grease-able.
I use bleach and Simple Cherry on the house. Works extremely well but bleach is a little difficult to find right now. For the house, this year I resorted to Pool bleach found at Walmart. Probably pretty old as it seemed weak. I generally use the Chlorox brand and use 4 gallons of bleach with 2 scoops of Simple Cherry downstreamed using my pressure washer with a large 0 deg tip to reduce pressure. Can still reach top of 2nd story. House is vinyl sided.