Optima, you make a very good point about reporting. Without knowing how many are using ONR successfully and unsuccessfully it would be hard to know if ONR is causing a problem. I guess the other dimension is how much ONR is being used in the cases where people have problems. If someone is say pouring in half a bottle then I would not be surprised if this had consequences .
The standard dilution of ONR is 256:1, no idea how big the capacity of your steamers are but would assume to keep this ratio then only a small amount of ONR would be required. ONR will soften water and I think Yvan has talked about ONR helping descale in the interior of the steamer and so some caution is required if using ONR in an old steamer.
Having said all of this, I do respect the wishes of any manufacturer and so if your view is not to use anything other than clean water then fair enough.
I am sure we would all love to see some data on how many are using ONR in a steamer and any issues they are facing.
One solution is to test ONR in the lab but I know you are all very busy so just send me two (top of the range) steamers so I can do side by side testing Oh, I do not have a car at the moment so if you could also send me one, it would be very helpful! I know it would not be cheap to send two steamers and a car to the UK but can one put a price on scientific testing?