Thats the product that i use, but there is lots of different ones out there on the market that do the same job. Webseal make silicone mainly, but also do bolt on products, make a very good trade glass cleaner. The place that i buy it from is a small plastic supllier, they supply plastic trims, fascia, soffit, guttering ect. Thats where you will find the sort of stuff for definate! Werth, think thats how you spell it also make it, they do lots of products for the building industry. If your doing a big job, i would recommend using the cleaner on the frames and the glass, but using different pieces of tissue on each. Then when you have cleaned the glass with the solvent and it is dry, spray with a glass cleaner and buff up. Takes a while, but your customers will be well chuffed, and if your going back to clean the windows in future, will make your job so much easier!!!