You've hit on one of my favourite topics
Like many, I'd recieved free samples from OneStep over the years, but couldn't make it work for me, so threw the bottle to the back of the garage. After a few different cleaning shows, I had quite a small collection of samples. One day, during a garage clear out, I decided to give it one last chance after reading on another forum of the success people were having with it on upholstery. Spray on, agitate really well and rinse. Hey presto, it works
I find the best way for carpets and upholstery are:
a) It works better hot. The hotter the better.
b) Agitate, agitate, agitate. Brushes, towels or pads on upholstery, rotary or dry powder (host type) machine on carpets.
c) You only need a freshwater rinse. Acid rinse only for technical reasons, not required for cleaning.
d) The Woolsafe approved product (Fineline) will perform equally as well in the real world as the regular product, which is theoretically about 2-3% more efficient.
Last weekend, we bonnet cleaned a 40,000sq.ft. office block with OneStep. The results were superb and we also took out about 50 BlueTac/gum wads with it. It is a very versatile product.
As you don't run OneStep through your machine, you shouldn't have a corrosion problem. The Fineline is, however, slightly acidic so it wears the sprayer's brass jets. (mine last about 9 months).
OneStep has just gone up quite significantly. I think you'll find it costs £85 for 4x5litres, not 1x5ltr. A few months ago I posted elsewhere of a costing I did on carpets only with 5 litres of product. It worked out at a little over 2p per sq.M with a product cost of £15.50 per 5 ltrs. So it's gone up a bit now, but still less than 3p I think. And there's no rinse solution to pay for.
OneStep would appear to be one of the safest products on the market (food grade ingredients) and I find that the customers love the appeal of a chemical free freshwater rinse.
Give it a try. Most people have to try hard to make it work for them, but it's worth it.